summaryrefslogtreecommitdiff
path: root/kernel/rcu/tree.c
blob: d80e0d2f68c675de3d95a89ad22a09465a2a995b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
/*
 * Read-Copy Update mechanism for mutual exclusion
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
 *
 * Copyright IBM Corporation, 2008
 *
 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
 *	    Manfred Spraul <manfred@colorfullife.com>
 *	    Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
 *
 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 *	Documentation/RCU
 */
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/nmi.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/export.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/time.h>
#include <linux/kernel_stat.h>
#include <linux/wait.h>
#include <linux/kthread.h>
#include <linux/prefetch.h>
#include <linux/delay.h>
#include <linux/stop_machine.h>
#include <linux/random.h>
#include <linux/trace_events.h>
#include <linux/suspend.h>

#include "tree.h"
#include "rcu.h"

#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "rcutree."

/* Data structures. */

/*
 * In order to export the rcu_state name to the tracing tools, it
 * needs to be added in the __tracepoint_string section.
 * This requires defining a separate variable tp_<sname>_varname
 * that points to the string being used, and this will allow
 * the tracing userspace tools to be able to decipher the string
 * address to the matching string.
 */
#ifdef CONFIG_TRACING
# define DEFINE_RCU_TPS(sname) \
static char sname##_varname[] = #sname; \
static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
# define RCU_STATE_NAME(sname) sname##_varname
#else
# define DEFINE_RCU_TPS(sname)
# define RCU_STATE_NAME(sname) __stringify(sname)
#endif

#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
DEFINE_RCU_TPS(sname) \
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
struct rcu_state sname##_state = { \
	.level = { &sname##_state.node[0] }, \
	.rda = &sname##_data, \
	.call = cr, \
	.gp_state = RCU_GP_IDLE, \
	.gpnum = 0UL - 300UL, \
	.completed = 0UL - 300UL, \
	.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
	.orphan_nxttail = &sname##_state.orphan_nxtlist, \
	.orphan_donetail = &sname##_state.orphan_donelist, \
	.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
	.name = RCU_STATE_NAME(sname), \
	.abbr = sabbr, \
	.exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \
	.exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \
}

RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);

static struct rcu_state *const rcu_state_p;
LIST_HEAD(rcu_struct_flavors);

/* Dump rcu_node combining tree at boot to verify correct setup. */
static bool dump_tree;
module_param(dump_tree, bool, 0444);
/* Control rcu_node-tree auto-balancing at boot time. */
static bool rcu_fanout_exact;
module_param(rcu_fanout_exact, bool, 0444);
/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
module_param(rcu_fanout_leaf, int, 0444);
int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
/* Number of rcu_nodes at specified level. */
static int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
/* panic() on RCU Stall sysctl. */
int sysctl_panic_on_rcu_stall __read_mostly;

/*
 * The rcu_scheduler_active variable is initialized to the value
 * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
 * first task is spawned.  So when this variable is RCU_SCHEDULER_INACTIVE,
 * RCU can assume that there is but one task, allowing RCU to (for example)
 * optimize synchronize_rcu() to a simple barrier().  When this variable
 * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
 * to detect real grace periods.  This variable is also used to suppress
 * boot-time false positives from lockdep-RCU error checking.  Finally, it
 * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
 * is fully initialized, including all of its kthreads having been spawned.
 */
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);

/*
 * The rcu_scheduler_fully_active variable transitions from zero to one
 * during the early_initcall() processing, which is after the scheduler
 * is capable of creating new tasks.  So RCU processing (for example,
 * creating tasks for RCU priority boosting) must be delayed until after
 * rcu_scheduler_fully_active transitions from zero to one.  We also
 * currently delay invocation of any RCU callbacks until after this point.
 *
 * It might later prove better for people registering RCU callbacks during
 * early boot to take responsibility for these callbacks, but one step at
 * a time.
 */
static int rcu_scheduler_fully_active __read_mostly;

static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
static void invoke_rcu_core(void);
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
static void rcu_report_exp_rdp(struct rcu_state *rsp,
			       struct rcu_data *rdp, bool wake);
static void sync_sched_exp_online_cleanup(int cpu);

/* rcuc/rcub kthread realtime priority */
#ifdef CONFIG_RCU_KTHREAD_PRIO
static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
#else /* #ifdef CONFIG_RCU_KTHREAD_PRIO */
static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
#endif /* #else #ifdef CONFIG_RCU_KTHREAD_PRIO */
module_param(kthread_prio, int, 0644);

/* Delay in jiffies for grace-period initialization delays, debug only. */

#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT
static int gp_preinit_delay = CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT_DELAY;
module_param(gp_preinit_delay, int, 0644);
#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
static const int gp_preinit_delay;
#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */

#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT
static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY;
module_param(gp_init_delay, int, 0644);
#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
static const int gp_init_delay;
#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */

#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP
static int gp_cleanup_delay = CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY;
module_param(gp_cleanup_delay, int, 0644);
#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
static const int gp_cleanup_delay;
#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */

/*
 * Number of grace periods between delays, normalized by the duration of
 * the delay.  The longer the the delay, the more the grace periods between
 * each delay.  The reason for this normalization is that it means that,
 * for non-zero delays, the overall slowdown of grace periods is constant
 * regardless of the duration of the delay.  This arrangement balances
 * the need for long delays to increase some race probabilities with the
 * need for fast grace periods to increase other race probabilities.
 */
#define PER_RCU_NODE_PERIOD 3	/* Number of grace periods between delays. */

/*
 * Track the rcutorture test sequence number and the update version
 * number within a given test.  The rcutorture_testseq is incremented
 * on every rcutorture module load and unload, so has an odd value
 * when a test is running.  The rcutorture_vernum is set to zero
 * when rcutorture starts and is incremented on each rcutorture update.
 * These variables enable correlating rcutorture output with the
 * RCU tracing information.
 */
unsigned long rcutorture_testseq;
unsigned long rcutorture_vernum;

/*
 * Compute the mask of online CPUs for the specified rcu_node structure.
 * This will not be stable unless the rcu_node structure's ->lock is
 * held, but the bit corresponding to the current CPU will be stable
 * in most contexts.
 */
unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
{
	return READ_ONCE(rnp->qsmaskinitnext);
}

/*
 * Return true if an RCU grace period is in progress.  The READ_ONCE()s
 * permit this function to be invoked without holding the root rcu_node
 * structure's ->lock, but of course results can be subject to change.
 */
static int rcu_gp_in_progress(struct rcu_state *rsp)
{
	return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum);
}

/*
 * Note a quiescent state.  Because we do not need to know
 * how many quiescent states passed, just if there was at least
 * one since the start of the grace period, this just sets a flag.
 * The caller must have disabled preemption.
 */
void rcu_sched_qs(void)
{
	if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
		return;
	trace_rcu_grace_period(TPS("rcu_sched"),
			       __this_cpu_read(rcu_sched_data.gpnum),
			       TPS("cpuqs"));
	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
	if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
		return;
	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
	rcu_report_exp_rdp(&rcu_sched_state,
			   this_cpu_ptr(&rcu_sched_data), true);
}

void rcu_bh_qs(void)
{
	if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
		trace_rcu_grace_period(TPS("rcu_bh"),
				       __this_cpu_read(rcu_bh_data.gpnum),
				       TPS("cpuqs"));
		__this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
	}
}

static DEFINE_PER_CPU(int, rcu_sched_qs_mask);

static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
	.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
	.dynticks = ATOMIC_INIT(1),
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
	.dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
	.dynticks_idle = ATOMIC_INIT(1),
#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
};

/*
 * Record entry into an extended quiescent state.  This is only to be
 * called when not already in an extended quiescent state.
 */
static void rcu_dynticks_eqs_enter(void)
{
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
	int special;

	/*
	 * CPUs seeing atomic_inc_return() must see prior RCU read-side
	 * critical sections, and we also must force ordering with the
	 * next idle sojourn.
	 */
	special = atomic_inc_return(&rdtp->dynticks);
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && special & 0x1);
}

/*
 * Record exit from an extended quiescent state.  This is only to be
 * called from an extended quiescent state.
 */
static void rcu_dynticks_eqs_exit(void)
{
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
	int special;

	/*
	 * CPUs seeing atomic_inc_return() must see prior idle sojourns,
	 * and we also must force ordering with the next RCU read-side
	 * critical section.
	 */
	special = atomic_inc_return(&rdtp->dynticks);
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(special & 0x1));
}

/*
 * Reset the current CPU's ->dynticks counter to indicate that the
 * newly onlined CPU is no longer in an extended quiescent state.
 * This will either leave the counter unchanged, or increment it
 * to the next non-quiescent value.
 *
 * The non-atomic test/increment sequence works because the upper bits
 * of the ->dynticks counter are manipulated only by the corresponding CPU,
 * or when the corresponding CPU is offline.
 */
static void rcu_dynticks_eqs_online(void)
{
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

	if (atomic_read(&rdtp->dynticks) & 0x1)
		return;
	atomic_add(0x1, &rdtp->dynticks);
}

/*
 * Is the current CPU in an extended quiescent state?
 *
 * No ordering, as we are sampling CPU-local information.
 */
bool rcu_dynticks_curr_cpu_in_eqs(void)
{
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

	return !(atomic_read(&rdtp->dynticks) & 0x1);
}

/*
 * Snapshot the ->dynticks counter with full ordering so as to allow
 * stable comparison of this counter with past and future snapshots.
 */
int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
{
	int snap = atomic_add_return(0, &rdtp->dynticks);

	return snap;
}

/*
 * Return true if the snapshot returned from rcu_dynticks_snap()
 * indicates that RCU is in an extended quiescent state.
 */
static bool rcu_dynticks_in_eqs(int snap)
{
	return !(snap & 0x1);
}

/*
 * Return true if the CPU corresponding to the specified rcu_dynticks
 * structure has spent some time in an extended quiescent state since
 * rcu_dynticks_snap() returned the specified snapshot.
 */
static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
{
	return snap != rcu_dynticks_snap(rdtp);
}

/*
 * Do a double-increment of the ->dynticks counter to emulate a
 * momentary idle-CPU quiescent state.
 */
static void rcu_dynticks_momentary_idle(void)
{
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
	int special = atomic_add_return(2, &rdtp->dynticks);

	/* It is illegal to call this from idle state. */
	WARN_ON_ONCE(!(special & 0x1));
}

DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);

/*
 * Let the RCU core know that this CPU has gone through the scheduler,
 * which is a quiescent state.  This is called when the need for a
 * quiescent state is urgent, so we burn an atomic operation and full
 * memory barriers to let the RCU core know about it, regardless of what
 * this CPU might (or might not) do in the near future.
 *
 * We inform the RCU core by emulating a zero-duration dyntick-idle
 * period, which we in turn do by incrementing the ->dynticks counter
 * by two.
 *
 * The caller must have disabled interrupts.
 */
static void rcu_momentary_dyntick_idle(void)
{
	struct rcu_data *rdp;
	int resched_mask;
	struct rcu_state *rsp;

	/*
	 * Yes, we can lose flag-setting operations.  This is OK, because
	 * the flag will be set again after some delay.
	 */
	resched_mask = raw_cpu_read(rcu_sched_qs_mask);
	raw_cpu_write(rcu_sched_qs_mask, 0);

	/* Find the flavor that needs a quiescent state. */
	for_each_rcu_flavor(rsp) {
		rdp = raw_cpu_ptr(rsp->rda);
		if (!(resched_mask & rsp->flavor_mask))
			continue;
		smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */
		if (READ_ONCE(rdp->mynode->completed) !=
		    READ_ONCE(rdp->cond_resched_completed))
			continue;

		/*
		 * Pretend to be momentarily idle for the quiescent state.
		 * This allows the grace-period kthread to record the
		 * quiescent state, with no need for this CPU to do anything
		 * further.
		 */
		rcu_dynticks_momentary_idle();
		break;
	}
}

/*
 * Note a context switch.  This is a quiescent state for RCU-sched,
 * and requires special handling for preemptible RCU.
 * The caller must have disabled interrupts.
 */
void rcu_note_context_switch(void)
{
	barrier(); /* Avoid RCU read-side critical sections leaking down. */
	trace_rcu_utilization(TPS("Start context switch"));
	rcu_sched_qs();
	rcu_preempt_note_context_switch();
	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
		rcu_momentary_dyntick_idle();
	trace_rcu_utilization(TPS("End context switch"));
	barrier(); /* Avoid RCU read-side critical sections leaking up. */
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);

/*
 * Register a quiescent state for all RCU flavors.  If there is an
 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
 * dyntick-idle quiescent state visible to other CPUs (but only for those
 * RCU flavors in desperate need of a quiescent state, which will normally
 * be none of them).  Either way, do a lightweight quiescent state for
 * all RCU flavors.
 *
 * The barrier() calls are redundant in the common case when this is
 * called externally, but just in case this is called from within this
 * file.
 *
 */
void rcu_all_qs(void)
{
	unsigned long flags;

	barrier(); /* Avoid RCU read-side critical sections leaking down. */
	if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) {
		local_irq_save(flags);
		rcu_momentary_dyntick_idle();
		local_irq_restore(flags);
	}
	if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))) {
		/*
		 * Yes, we just checked a per-CPU variable with preemption
		 * enabled, so we might be migrated to some other CPU at
		 * this point.  That is OK because in that case, the
		 * migration will supply the needed quiescent state.
		 * We might end up needlessly disabling preemption and
		 * invoking rcu_sched_qs() on the destination CPU, but
		 * the probability and cost are both quite low, so this
		 * should not be a problem in practice.
		 */
		preempt_disable();
		rcu_sched_qs();
		preempt_enable();
	}
	this_cpu_inc(rcu_qs_ctr);
	barrier(); /* Avoid RCU read-side critical sections leaking up. */
}
EXPORT_SYMBOL_GPL(rcu_all_qs);

static long blimit = 10;	/* Maximum callbacks per rcu_do_batch. */
static long qhimark = 10000;	/* If this many pending, ignore blimit. */
static long qlowmark = 100;	/* Once only this many pending, use blimit. */

module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);

static ulong jiffies_till_first_fqs = ULONG_MAX;
static ulong jiffies_till_next_fqs = ULONG_MAX;
static bool rcu_kick_kthreads;

module_param(jiffies_till_first_fqs, ulong, 0644);
module_param(jiffies_till_next_fqs, ulong, 0644);
module_param(rcu_kick_kthreads, bool, 0644);

/*
 * How long the grace period must be before we start recruiting
 * quiescent-state help from rcu_note_context_switch().
 */
static ulong jiffies_till_sched_qs = HZ / 20;
module_param(jiffies_till_sched_qs, ulong, 0644);

static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
				  struct rcu_data *rdp);
static void force_qs_rnp(struct rcu_state *rsp,
			 int (*f)(struct rcu_data *rsp, bool *isidle,
				  unsigned long *maxj),
			 bool *isidle, unsigned long *maxj);
static void force_quiescent_state(struct rcu_state *rsp);
static int rcu_pending(void);

/*
 * Return the number of RCU batches started thus far for debug & stats.
 */
unsigned long rcu_batches_started(void)
{
	return rcu_state_p->gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started);

/*
 * Return the number of RCU-sched batches started thus far for debug & stats.
 */
unsigned long rcu_batches_started_sched(void)
{
	return rcu_sched_state.gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started_sched);

/*
 * Return the number of RCU BH batches started thus far for debug & stats.
 */
unsigned long rcu_batches_started_bh(void)
{
	return rcu_bh_state.gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started_bh);

/*
 * Return the number of RCU batches completed thus far for debug & stats.
 */
unsigned long rcu_batches_completed(void)
{
	return rcu_state_p->completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);

/*
 * Return the number of RCU-sched batches completed thus far for debug & stats.
 */
unsigned long rcu_batches_completed_sched(void)
{
	return rcu_sched_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);

/*
 * Return the number of RCU BH batches completed thus far for debug & stats.
 */
unsigned long rcu_batches_completed_bh(void)
{
	return rcu_bh_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);

/*
 * Return the number of RCU expedited batches completed thus far for
 * debug & stats.  Odd numbers mean that a batch is in progress, even
 * numbers mean idle.  The value returned will thus be roughly double
 * the cumulative batches since boot.
 */
unsigned long rcu_exp_batches_completed(void)
{
	return rcu_state_p->expedited_sequence;
}
EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);

/*
 * Return the number of RCU-sched expedited batches completed thus far
 * for debug & stats.  Similar to rcu_exp_batches_completed().
 */
unsigned long rcu_exp_batches_completed_sched(void)
{
	return rcu_sched_state.expedited_sequence;
}
EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched);

/*
 * Force a quiescent state.
 */
void rcu_force_quiescent_state(void)
{
	force_quiescent_state(rcu_state_p);
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

/*
 * Force a quiescent state for RCU BH.
 */
void rcu_bh_force_quiescent_state(void)
{
	force_quiescent_state(&rcu_bh_state);
}
EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);

/*
 * Force a quiescent state for RCU-sched.
 */
void rcu_sched_force_quiescent_state(void)
{
	force_quiescent_state(&rcu_sched_state);
}
EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);

/*
 * Show the state of the grace-period kthreads.
 */
void show_rcu_gp_kthreads(void)
{
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp) {
		pr_info("%s: wait state: %d ->state: %#lx\n",
			rsp->name, rsp->gp_state, rsp->gp_kthread->state);
		/* sched_show_task(rsp->gp_kthread); */
	}
}
EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);

/*
 * Record the number of times rcutorture tests have been initiated and
 * terminated.  This information allows the debugfs tracing stats to be
 * correlated to the rcutorture messages, even when the rcutorture module
 * is being repeatedly loaded and unloaded.  In other words, we cannot
 * store this state in rcutorture itself.
 */
void rcutorture_record_test_transition(void)
{
	rcutorture_testseq++;
	rcutorture_vernum = 0;
}
EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);

/*
 * Send along grace-period-related data for rcutorture diagnostics.
 */
void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
			    unsigned long *gpnum, unsigned long *completed)
{
	struct rcu_state *rsp = NULL;

	switch (test_type) {
	case RCU_FLAVOR:
		rsp = rcu_state_p;
		break;
	case RCU_BH_FLAVOR:
		rsp = &rcu_bh_state;
		break;
	case RCU_SCHED_FLAVOR:
		rsp = &rcu_sched_state;
		break;
	default:
		break;
	}
	if (rsp != NULL) {
		*flags = READ_ONCE(rsp->gp_flags);
		*gpnum = READ_ONCE(rsp->gpnum);
		*completed = READ_ONCE(rsp->completed);
		return;
	}
	*flags = 0;
	*gpnum = 0;
	*completed = 0;
}
EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);

/*
 * Record the number of writer passes through the current rcutorture test.
 * This is also used to correlate debugfs tracing stats with the rcutorture
 * messages.
 */
void rcutorture_record_progress(unsigned long vernum)
{
	rcutorture_vernum++;
}
EXPORT_SYMBOL_GPL(rcutorture_record_progress);

/*
 * Does the CPU have callbacks ready to be invoked?
 */
static int
cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
{
	return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
	       rdp->nxttail[RCU_NEXT_TAIL] != NULL;
}

/*
 * Return the root node of the specified rcu_state structure.
 */
static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
{
	return &rsp->node[0];
}

/*
 * Is there any need for future grace periods?
 * Interrupts must be disabled.  If the caller does not hold the root
 * rnp_node structure's ->lock, the results are advisory only.
 */
static int rcu_future_needs_gp(struct rcu_state *rsp)
{
	struct rcu_node *rnp = rcu_get_root(rsp);
	int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
	int *fp = &rnp->need_future_gp[idx];

	return READ_ONCE(*fp);
}

/*
 * Does the current CPU require a not-yet-started grace period?
 * The caller must have disabled interrupts to prevent races with
 * normal callback registry.
 */
static bool
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
	int i;

	if (rcu_gp_in_progress(rsp))
		return false;  /* No, a grace period is already in progress. */
	if (rcu_future_needs_gp(rsp))
		return true;  /* Yes, a no-CBs CPU needs one. */
	if (!rdp->nxttail[RCU_NEXT_TAIL])
		return false;  /* No, this is a no-CBs (or offline) CPU. */
	if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
		return true;  /* Yes, CPU has newly registered callbacks. */
	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
		if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
		    ULONG_CMP_LT(READ_ONCE(rsp->completed),
				 rdp->nxtcompleted[i]))
			return true;  /* Yes, CBs for future grace period. */
	return false; /* No grace period needed. */
}

/*
 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
 *
 * If the new value of the ->dynticks_nesting counter now is zero,
 * we really have entered idle, and must do the appropriate accounting.
 * The caller must have disabled interrupts.
 */
static void rcu_eqs_enter_common(long long oldval, bool user)
{
	struct rcu_state *rsp;
	struct rcu_data *rdp;
	RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)

	trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
	if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
	    !user && !is_idle_task(current)) {
		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());

		trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
		rcu_ftrace_dump(DUMP_ORIG);
		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
			  current->pid, current->comm,
			  idle->pid, idle->comm); /* must be idle task! */
	}
	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		do_nocb_deferred_wakeup(rdp);
	}
	rcu_prepare_for_idle();
	rcu_dynticks_eqs_enter();
	rcu_dynticks_task_enter();

	/*
	 * It is illegal to enter an extended quiescent state while
	 * in an RCU read-side critical section.
	 */
	RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
			 "Illegal idle entry in RCU read-side critical section.");
	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),
			 "Illegal idle entry in RCU-bh read-side critical section.");
	RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),
			 "Illegal idle entry in RCU-sched read-side critical section.");
}

/*
 * Enter an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
 */
static void rcu_eqs_enter(bool user)
{
	long long oldval;
	struct rcu_dynticks *rdtp;

	rdtp = this_cpu_ptr(&rcu_dynticks);
	oldval = rdtp->dynticks_nesting;
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
		     (oldval & DYNTICK_TASK_NEST_MASK) == 0);
	if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
		rdtp->dynticks_nesting = 0;
		rcu_eqs_enter_common(oldval, user);
	} else {
		rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
	}
}

/**
 * rcu_idle_enter - inform RCU that current CPU is entering idle
 *
 * Enter idle mode, in other words, -leave- the mode in which RCU
 * read-side critical sections can occur.  (Though RCU read-side
 * critical sections can occur in irq handlers in idle, a possibility
 * handled by irq_enter() and irq_exit().)
 *
 * We crowbar the ->dynticks_nesting field to zero to allow for
 * the possibility of usermode upcalls having messed up our count
 * of interrupt nesting level during the prior busy period.
 */
void rcu_idle_enter(void)
{
	unsigned long flags;

	local_irq_save(flags);
	rcu_eqs_enter(false);
	rcu_sysidle_enter(0);
	local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);

#ifdef CONFIG_NO_HZ_FULL
/**
 * rcu_user_enter - inform RCU that we are resuming userspace.
 *
 * Enter RCU idle mode right before resuming userspace.  No use of RCU
 * is permitted between this call and rcu_user_exit(). This way the
 * CPU doesn't need to maintain the tick for RCU maintenance purposes
 * when the CPU runs in userspace.
 */
void rcu_user_enter(void)
{
	rcu_eqs_enter(1);
}
#endif /* CONFIG_NO_HZ_FULL */

/**
 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
 *
 * Exit from an interrupt handler, which might possibly result in entering
 * idle mode, in other words, leaving the mode in which read-side critical
 * sections can occur.  The caller must have disabled interrupts.
 *
 * This code assumes that the idle loop never does anything that might
 * result in unbalanced calls to irq_enter() and irq_exit().  If your
 * architecture violates this assumption, RCU will give you what you
 * deserve, good and hard.  But very infrequently and irreproducibly.
 *
 * Use things like work queues to work around this limitation.
 *
 * You have been warned.
 */
void rcu_irq_exit(void)
{
	long long oldval;
	struct rcu_dynticks *rdtp;

	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!");
	rdtp = this_cpu_ptr(&rcu_dynticks);
	oldval = rdtp->dynticks_nesting;
	rdtp->dynticks_nesting--;
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
		     rdtp->dynticks_nesting < 0);
	if (rdtp->dynticks_nesting)
		trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
	else
		rcu_eqs_enter_common(oldval, true);
	rcu_sysidle_enter(1);
}

/*
 * Wrapper for rcu_irq_exit() where interrupts are enabled.
 */
void rcu_irq_exit_irqson(void)
{
	unsigned long flags;

	local_irq_save(flags);
	rcu_irq_exit();
	local_irq_restore(flags);
}

/*
 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
 *
 * If the new value of the ->dynticks_nesting counter was previously zero,
 * we really have exited idle, and must do the appropriate accounting.
 * The caller must have disabled interrupts.
 */
static void rcu_eqs_exit_common(long long oldval, int user)
{
	RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)

	rcu_dynticks_task_exit();
	rcu_dynticks_eqs_exit();
	rcu_cleanup_after_idle();
	trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
	if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
	    !user && !is_idle_task(current)) {
		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());

		trace_rcu_dyntick(TPS("Error on exit: not idle task"),
				  oldval, rdtp->dynticks_nesting);
		rcu_ftrace_dump(DUMP_ORIG);
		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
			  current->pid, current->comm,
			  idle->pid, idle->comm); /* must be idle task! */
	}
}

/*
 * Exit an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
 */
static void rcu_eqs_exit(bool user)
{
	struct rcu_dynticks *rdtp;
	long long oldval;

	rdtp = this_cpu_ptr(&rcu_dynticks);
	oldval = rdtp->dynticks_nesting;
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
	if (oldval & DYNTICK_TASK_NEST_MASK) {
		rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
	} else {
		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
		rcu_eqs_exit_common(oldval, user);
	}
}

/**
 * rcu_idle_exit - inform RCU that current CPU is leaving idle
 *
 * Exit idle mode, in other words, -enter- the mode in which RCU
 * read-side critical sections can occur.
 *
 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
 * allow for the possibility of usermode upcalls messing up our count
 * of interrupt nesting level during the busy period that is just
 * now starting.
 */
void rcu_idle_exit(void)
{
	unsigned long flags;

	local_irq_save(flags);
	rcu_eqs_exit(false);
	rcu_sysidle_exit(0);
	local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);

#ifdef CONFIG_NO_HZ_FULL
/**
 * rcu_user_exit - inform RCU that we are exiting userspace.
 *
 * Exit RCU idle mode while entering the kernel because it can
 * run a RCU read side critical section anytime.
 */
void rcu_user_exit(void)
{
	rcu_eqs_exit(1);
}
#endif /* CONFIG_NO_HZ_FULL */

/**
 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
 *
 * Enter an interrupt handler, which might possibly result in exiting
 * idle mode, in other words, entering the mode in which read-side critical
 * sections can occur.  The caller must have disabled interrupts.
 *
 * Note that the Linux kernel is fully capable of entering an interrupt
 * handler that it never exits, for example when doing upcalls to
 * user mode!  This code assumes that the idle loop never does upcalls to
 * user mode.  If your architecture does do upcalls from the idle loop (or
 * does anything else that results in unbalanced calls to the irq_enter()
 * and irq_exit() functions), RCU will give you what you deserve, good
 * and hard.  But very infrequently and irreproducibly.
 *
 * Use things like work queues to work around this limitation.
 *
 * You have been warned.
 */
void rcu_irq_enter(void)
{
	struct rcu_dynticks *rdtp;
	long long oldval;

	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!");
	rdtp = this_cpu_ptr(&rcu_dynticks);
	oldval = rdtp->dynticks_nesting;
	rdtp->dynticks_nesting++;
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
		     rdtp->dynticks_nesting == 0);
	if (oldval)
		trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
	else
		rcu_eqs_exit_common(oldval, true);
	rcu_sysidle_exit(1);
}

/*
 * Wrapper for rcu_irq_enter() where interrupts are enabled.
 */
void rcu_irq_enter_irqson(void)
{
	unsigned long flags;

	local_irq_save(flags);
	rcu_irq_enter();
	local_irq_restore(flags);
}

/**
 * rcu_nmi_enter - inform RCU of entry to NMI context
 *
 * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
 * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
 * that the CPU is active.  This implementation permits nested NMIs, as
 * long as the nesting level does not overflow an int.  (You will probably
 * run out of stack space first.)
 */
void rcu_nmi_enter(void)
{
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
	int incby = 2;

	/* Complain about underflow. */
	WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);

	/*
	 * If idle from RCU viewpoint, atomically increment ->dynticks
	 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
	 * Otherwise, increment ->dynticks_nmi_nesting by two.  This means
	 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
	 * to be in the outermost NMI handler that interrupted an RCU-idle
	 * period (observation due to Andy Lutomirski).
	 */
	if (rcu_dynticks_curr_cpu_in_eqs()) {
		rcu_dynticks_eqs_exit();
		incby = 1;
	}
	rdtp->dynticks_nmi_nesting += incby;
	barrier();
}

/**
 * rcu_nmi_exit - inform RCU of exit from NMI context
 *
 * If we are returning from the outermost NMI handler that interrupted an
 * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
 * to let the RCU grace-period handling know that the CPU is back to
 * being RCU-idle.
 */
void rcu_nmi_exit(void)
{
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

	/*
	 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
	 * (We are exiting an NMI handler, so RCU better be paying attention
	 * to us!)
	 */
	WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
	WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());

	/*
	 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
	 * leave it in non-RCU-idle state.
	 */
	if (rdtp->dynticks_nmi_nesting != 1) {
		rdtp->dynticks_nmi_nesting -= 2;
		return;
	}

	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
	rdtp->dynticks_nmi_nesting = 0;
	rcu_dynticks_eqs_enter();
}

/**
 * __rcu_is_watching - are RCU read-side critical sections safe?
 *
 * Return true if RCU is watching the running CPU, which means that
 * this CPU can safely enter RCU read-side critical sections.  Unlike
 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
 * least disabled preemption.
 */
bool notrace __rcu_is_watching(void)
{
	return !rcu_dynticks_curr_cpu_in_eqs();
}

/**
 * rcu_is_watching - see if RCU thinks that the current CPU is idle
 *
 * If the current CPU is in its idle loop and is neither in an interrupt
 * or NMI handler, return true.
 */
bool notrace rcu_is_watching(void)
{
	bool ret;

	preempt_disable_notrace();
	ret = __rcu_is_watching();
	preempt_enable_notrace();
	return ret;
}
EXPORT_SYMBOL_GPL(rcu_is_watching);

#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)

/*
 * Is the current CPU online?  Disable preemption to avoid false positives
 * that could otherwise happen due to the current CPU number being sampled,
 * this task being preempted, its old CPU being taken offline, resuming
 * on some other CPU, then determining that its old CPU is now offline.
 * It is OK to use RCU on an offline processor during initial boot, hence
 * the check for rcu_scheduler_fully_active.  Note also that it is OK
 * for a CPU coming online to use RCU for one jiffy prior to marking itself
 * online in the cpu_online_mask.  Similarly, it is OK for a CPU going
 * offline to continue to use RCU for one jiffy after marking itself
 * offline in the cpu_online_mask.  This leniency is necessary given the
 * non-atomic nature of the online and offline processing, for example,
 * the fact that a CPU enters the scheduler after completing the teardown
 * of the CPU.
 *
 * This is also why RCU internally marks CPUs online during in the
 * preparation phase and offline after the CPU has been taken down.
 *
 * Disable checking if in an NMI handler because we cannot safely report
 * errors from NMI handlers anyway.
 */
bool rcu_lockdep_current_cpu_online(void)
{
	struct rcu_data *rdp;
	struct rcu_node *rnp;
	bool ret;

	if (in_nmi())
		return true;
	preempt_disable();
	rdp = this_cpu_ptr(&rcu_sched_data);
	rnp = rdp->mynode;
	ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
	      !rcu_scheduler_fully_active;
	preempt_enable();
	return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);

#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */

/**
 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
 *
 * If the current CPU is idle or running at a first-level (not nested)
 * interrupt from idle, return true.  The caller must have at least
 * disabled preemption.
 */
static int rcu_is_cpu_rrupt_from_idle(void)
{
	return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
}

/*
 * Snapshot the specified CPU's dynticks counter so that we can later
 * credit them with an implicit quiescent state.  Return 1 if this CPU
 * is in dynticks idle mode, which is an extended quiescent state.
 */
static int dyntick_save_progress_counter(struct rcu_data *rdp,
					 bool *isidle, unsigned long *maxj)
{
	rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
	rcu_sysidle_check_cpu(rdp, isidle, maxj);
	if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
		if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
				 rdp->mynode->gpnum))
			WRITE_ONCE(rdp->gpwrap, true);
		return 1;
	}
	return 0;
}

/*
 * Return true if the specified CPU has passed through a quiescent
 * state by virtue of being in or having passed through an dynticks
 * idle state since the last call to dyntick_save_progress_counter()
 * for this same CPU, or by virtue of having been offline.
 */
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
				    bool *isidle, unsigned long *maxj)
{
	unsigned long jtsq;
	int *rcrmp;
	unsigned long rjtsc;
	struct rcu_node *rnp;

	/*
	 * If the CPU passed through or entered a dynticks idle phase with
	 * no active irq/NMI handlers, then we can safely pretend that the CPU
	 * already acknowledged the request to pass through a quiescent
	 * state.  Either way, that CPU cannot possibly be in an RCU
	 * read-side critical section that started before the beginning
	 * of the current RCU grace period.
	 */
	if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
		rdp->dynticks_fqs++;
		return 1;
	}

	/* Compute and saturate jiffies_till_sched_qs. */
	jtsq = jiffies_till_sched_qs;
	rjtsc = rcu_jiffies_till_stall_check();
	if (jtsq > rjtsc / 2) {
		WRITE_ONCE(jiffies_till_sched_qs, rjtsc);
		jtsq = rjtsc / 2;
	} else if (jtsq < 1) {
		WRITE_ONCE(jiffies_till_sched_qs, 1);
		jtsq = 1;
	}

	/*
	 * Has this CPU encountered a cond_resched_rcu_qs() since the
	 * beginning of the grace period?  For this to be the case,
	 * the CPU has to have noticed the current grace period.  This
	 * might not be the case for nohz_full CPUs looping in the kernel.
	 */
	rnp = rdp->mynode;
	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
	    READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_qs_ctr, rdp->cpu) &&
	    READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
		return 1;
	}

	/* Check for the CPU being offline. */
	if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) {
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
		rdp->offline_fqs++;
		return 1;
	}

	/*
	 * A CPU running for an extended time within the kernel can
	 * delay RCU grace periods.  When the CPU is in NO_HZ_FULL mode,
	 * even context-switching back and forth between a pair of
	 * in-kernel CPU-bound tasks cannot advance grace periods.
	 * So if the grace period is old enough, make the CPU pay attention.
	 * Note that the unsynchronized assignments to the per-CPU
	 * rcu_sched_qs_mask variable are safe.  Yes, setting of
	 * bits can be lost, but they will be set again on the next
	 * force-quiescent-state pass.  So lost bit sets do not result
	 * in incorrect behavior, merely in a grace period lasting
	 * a few jiffies longer than it might otherwise.  Because
	 * there are at most four threads involved, and because the
	 * updates are only once every few jiffies, the probability of
	 * lossage (and thus of slight grace-period extension) is
	 * quite low.
	 *
	 * Note that if the jiffies_till_sched_qs boot/sysfs parameter
	 * is set too high, we override with half of the RCU CPU stall
	 * warning delay.
	 */
	rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
	    time_after(jiffies, rdp->rsp->jiffies_resched)) {
		if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
			WRITE_ONCE(rdp->cond_resched_completed,
				   READ_ONCE(rdp->mynode->completed));
			smp_mb(); /* ->cond_resched_completed before *rcrmp. */
			WRITE_ONCE(*rcrmp,
				   READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
		}
		rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
	}

	/*
	 * If more than halfway to RCU CPU stall-warning time, do
	 * a resched_cpu() to try to loosen things up a bit.
	 */
	if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
		resched_cpu(rdp->cpu);

	return 0;
}

static void record_gp_stall_check_time(struct rcu_state *rsp)
{
	unsigned long j = jiffies;
	unsigned long j1;

	rsp->gp_start = j;
	smp_wmb(); /* Record start time before stall time. */
	j1 = rcu_jiffies_till_stall_check();
	WRITE_ONCE(rsp->jiffies_stall, j + j1);
	rsp->jiffies_resched = j + j1 / 2;
	rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
}

/*
 * Convert a ->gp_state value to a character string.
 */
static const char *gp_state_getname(short gs)
{
	if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
		return "???";
	return gp_state_names[gs];
}

/*
 * Complain about starvation of grace-period kthread.
 */
static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
{
	unsigned long gpa;
	unsigned long j;

	j = jiffies;
	gpa = READ_ONCE(rsp->gp_activity);
	if (j - gpa > 2 * HZ) {
		pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx\n",
		       rsp->name, j - gpa,
		       rsp->gpnum, rsp->completed,
		       rsp->gp_flags,
		       gp_state_getname(rsp->gp_state), rsp->gp_state,
		       rsp->gp_kthread ? rsp->gp_kthread->state : ~0);
		if (rsp->gp_kthread) {
			sched_show_task(rsp->gp_kthread);
			wake_up_process(rsp->gp_kthread);
		}
	}
}

/*
 * Dump stacks of all tasks running on stalled CPUs.  First try using
 * NMIs, but fall back to manual remote stack tracing on architectures
 * that don't support NMI-based stack dumps.  The NMI-triggered stack
 * traces are more accurate because they are printed by the target CPU.
 */
static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
{
	int cpu;
	unsigned long flags;
	struct rcu_node *rnp;

	rcu_for_each_leaf_node(rsp, rnp) {
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		for_each_leaf_node_possible_cpu(rnp, cpu)
			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
				if (!trigger_single_cpu_backtrace(cpu))
					dump_cpu_task(cpu);
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
	}
}

/*
 * If too much time has passed in the current grace period, and if
 * so configured, go kick the relevant kthreads.
 */
static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
{
	unsigned long j;

	if (!rcu_kick_kthreads)
		return;
	j = READ_ONCE(rsp->jiffies_kick_kthreads);
	if (time_after(jiffies, j) && rsp->gp_kthread &&
	    (rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) {
		WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
		rcu_ftrace_dump(DUMP_ALL);
		wake_up_process(rsp->gp_kthread);
		WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);
	}
}

static inline void panic_on_rcu_stall(void)
{
	if (sysctl_panic_on_rcu_stall)
		panic("RCU Stall\n");
}

static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
{
	int cpu;
	long delta;
	unsigned long flags;
	unsigned long gpa;
	unsigned long j;
	int ndetected = 0;
	struct rcu_node *rnp = rcu_get_root(rsp);
	long totqlen = 0;

	/* Kick and suppress, if so configured. */
	rcu_stall_kick_kthreads(rsp);
	if (rcu_cpu_stall_suppress)
		return;

	/* Only let one CPU complain about others per time interval. */

	raw_spin_lock_irqsave_rcu_node(rnp, flags);
	delta = jiffies - READ_ONCE(rsp->jiffies_stall);
	if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		return;
	}
	WRITE_ONCE(rsp->jiffies_stall,
		   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

	/*
	 * OK, time to rat on our buddy...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
	pr_err("INFO: %s detected stalls on CPUs/tasks:",
	       rsp->name);
	print_cpu_stall_info_begin();
	rcu_for_each_leaf_node(rsp, rnp) {
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		ndetected += rcu_print_task_stall(rnp);
		if (rnp->qsmask != 0) {
			for_each_leaf_node_possible_cpu(rnp, cpu)
				if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
					print_cpu_stall_info(rsp, cpu);
					ndetected++;
				}
		}
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
	}

	print_cpu_stall_info_end();
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
	if (ndetected) {
		rcu_dump_cpu_stacks(rsp);

		/* Complain about tasks blocking the grace period. */
		rcu_print_detail_task_stall(rsp);
	} else {
		if (READ_ONCE(rsp->gpnum) != gpnum ||
		    READ_ONCE(rsp->completed) == gpnum) {
			pr_err("INFO: Stall ended before state dump start\n");
		} else {
			j = jiffies;
			gpa = READ_ONCE(rsp->gp_activity);
			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
			       rsp->name, j - gpa, j, gpa,
			       jiffies_till_next_fqs,
			       rcu_get_root(rsp)->qsmask);
			/* In this case, the current CPU might be at fault. */
			sched_show_task(current);
		}
	}

	rcu_check_gp_kthread_starvation(rsp);

	panic_on_rcu_stall();

	force_quiescent_state(rsp);  /* Kick them all. */
}

static void print_cpu_stall(struct rcu_state *rsp)
{
	int cpu;
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root(rsp);
	long totqlen = 0;

	/* Kick and suppress, if so configured. */
	rcu_stall_kick_kthreads(rsp);
	if (rcu_cpu_stall_suppress)
		return;

	/*
	 * OK, time to rat on ourselves...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
	pr_err("INFO: %s self-detected stall on CPU", rsp->name);
	print_cpu_stall_info_begin();
	print_cpu_stall_info(rsp, smp_processor_id());
	print_cpu_stall_info_end();
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
		jiffies - rsp->gp_start,
		(long)rsp->gpnum, (long)rsp->completed, totqlen);

	rcu_check_gp_kthread_starvation(rsp);

	rcu_dump_cpu_stacks(rsp);

	raw_spin_lock_irqsave_rcu_node(rnp, flags);
	if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
		WRITE_ONCE(rsp->jiffies_stall,
			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

	panic_on_rcu_stall();

	/*
	 * Attempt to revive the RCU machinery by forcing a context switch.
	 *
	 * A context switch would normally allow the RCU state machine to make
	 * progress and it could be we're stuck in kernel space without context
	 * switches for an entirely unreasonable amount of time.
	 */
	resched_cpu(smp_processor_id());
}

static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
	unsigned long completed;
	unsigned long gpnum;
	unsigned long gps;
	unsigned long j;
	unsigned long js;
	struct rcu_node *rnp;

	if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
	    !rcu_gp_in_progress(rsp))
		return;
	rcu_stall_kick_kthreads(rsp);
	j = jiffies;

	/*
	 * Lots of memory barriers to reject false positives.
	 *
	 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
	 * then rsp->gp_start, and finally rsp->completed.  These values
	 * are updated in the opposite order with memory barriers (or
	 * equivalent) during grace-period initialization and cleanup.
	 * Now, a false positive can occur if we get an new value of
	 * rsp->gp_start and a old value of rsp->jiffies_stall.  But given
	 * the memory barriers, the only way that this can happen is if one
	 * grace period ends and another starts between these two fetches.
	 * Detect this by comparing rsp->completed with the previous fetch
	 * from rsp->gpnum.
	 *
	 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
	 * and rsp->gp_start suffice to forestall false positives.
	 */
	gpnum = READ_ONCE(rsp->gpnum);
	smp_rmb(); /* Pick up ->gpnum first... */
	js = READ_ONCE(rsp->jiffies_stall);
	smp_rmb(); /* ...then ->jiffies_stall before the rest... */
	gps = READ_ONCE(rsp->gp_start);
	smp_rmb(); /* ...and finally ->gp_start before ->completed. */
	completed = READ_ONCE(rsp->completed);
	if (ULONG_CMP_GE(completed, gpnum) ||
	    ULONG_CMP_LT(j, js) ||
	    ULONG_CMP_GE(gps, js))
		return; /* No stall or GP completed since entering function. */
	rnp = rdp->mynode;
	if (rcu_gp_in_progress(rsp) &&
	    (READ_ONCE(rnp->qsmask) & rdp->grpmask)) {

		/* We haven't checked in, so go dump stack. */
		print_cpu_stall(rsp);

	} else if (rcu_gp_in_progress(rsp) &&
		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {

		/* They had a few time units to dump stack, so complain. */
		print_other_cpu_stall(rsp, gpnum);
	}
}

/**
 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
 *
 * Set the stall-warning timeout way off into the future, thus preventing
 * any RCU CPU stall-warning messages from appearing in the current set of
 * RCU grace periods.
 *
 * The caller must disable hard irqs.
 */
void rcu_cpu_stall_reset(void)
{
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
		WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
}

/*
 * Initialize the specified rcu_data structure's default callback list
 * to empty.  The default callback list is the one that is not used by
 * no-callbacks CPUs.
 */
static void init_default_callback_list(struct rcu_data *rdp)
{
	int i;

	rdp->nxtlist = NULL;
	for (i = 0; i < RCU_NEXT_SIZE; i++)
		rdp->nxttail[i] = &rdp->nxtlist;
}

/*
 * Initialize the specified rcu_data structure's callback list to empty.
 */
static void init_callback_list(struct rcu_data *rdp)
{
	if (init_nocb_callback_list(rdp))
		return;
	init_default_callback_list(rdp);
}

/*
 * Determine the value that ->completed will have at the end of the
 * next subsequent grace period.  This is used to tag callbacks so that
 * a CPU can invoke callbacks in a timely fashion even if that CPU has
 * been dyntick-idle for an extended period with callbacks under the
 * influence of RCU_FAST_NO_HZ.
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
				       struct rcu_node *rnp)
{
	/*
	 * If RCU is idle, we just wait for the next grace period.
	 * But we can only be sure that RCU is idle if we are looking
	 * at the root rcu_node structure -- otherwise, a new grace
	 * period might have started, but just not yet gotten around
	 * to initializing the current non-root rcu_node structure.
	 */
	if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
		return rnp->completed + 1;

	/*
	 * Otherwise, wait for a possible partial grace period and
	 * then the subsequent full grace period.
	 */
	return rnp->completed + 2;
}

/*
 * Trace-event helper function for rcu_start_future_gp() and
 * rcu_nocb_wait_gp().
 */
static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
				unsigned long c, const char *s)
{
	trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
				      rnp->completed, c, rnp->level,
				      rnp->grplo, rnp->grphi, s);
}

/*
 * Start some future grace period, as needed to handle newly arrived
 * callbacks.  The required future grace periods are recorded in each
 * rcu_node structure's ->need_future_gp field.  Returns true if there
 * is reason to awaken the grace-period kthread.
 *
 * The caller must hold the specified rcu_node structure's ->lock.
 */
static bool __maybe_unused
rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
		    unsigned long *c_out)
{
	unsigned long c;
	int i;
	bool ret = false;
	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);

	/*
	 * Pick up grace-period number for new callbacks.  If this
	 * grace period is already marked as needed, return to the caller.
	 */
	c = rcu_cbs_completed(rdp->rsp, rnp);
	trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
	if (rnp->need_future_gp[c & 0x1]) {
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
		goto out;
	}

	/*
	 * If either this rcu_node structure or the root rcu_node structure
	 * believe that a grace period is in progress, then we must wait
	 * for the one following, which is in "c".  Because our request
	 * will be noticed at the end of the current grace period, we don't
	 * need to explicitly start one.  We only do the lockless check
	 * of rnp_root's fields if the current rcu_node structure thinks
	 * there is no grace period in flight, and because we hold rnp->lock,
	 * the only possible change is when rnp_root's two fields are
	 * equal, in which case rnp_root->gpnum might be concurrently
	 * incremented.  But that is OK, as it will just result in our
	 * doing some extra useless work.
	 */
	if (rnp->gpnum != rnp->completed ||
	    READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
		rnp->need_future_gp[c & 0x1]++;
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
		goto out;
	}

	/*
	 * There might be no grace period in progress.  If we don't already
	 * hold it, acquire the root rcu_node structure's lock in order to
	 * start one (if needed).
	 */
	if (rnp != rnp_root)
		raw_spin_lock_rcu_node(rnp_root);

	/*
	 * Get a new grace-period number.  If there really is no grace
	 * period in progress, it will be smaller than the one we obtained
	 * earlier.  Adjust callbacks as needed.  Note that even no-CBs
	 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
	 */
	c = rcu_cbs_completed(rdp->rsp, rnp_root);
	for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
		if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
			rdp->nxtcompleted[i] = c;

	/*
	 * If the needed for the required grace period is already
	 * recorded, trace and leave.
	 */
	if (rnp_root->need_future_gp[c & 0x1]) {
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
		goto unlock_out;
	}

	/* Record the need for the future grace period. */
	rnp_root->need_future_gp[c & 0x1]++;

	/* If a grace period is not already in progress, start one. */
	if (rnp_root->gpnum != rnp_root->completed) {
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
	} else {
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
		ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
	}
unlock_out:
	if (rnp != rnp_root)
		raw_spin_unlock_rcu_node(rnp_root);
out:
	if (c_out != NULL)
		*c_out = c;
	return ret;
}

/*
 * Clean up any old requests for the just-ended grace period.  Also return
 * whether any additional grace periods have been requested.  Also invoke
 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
 * waiting for this grace period to complete.
 */
static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
	int c = rnp->completed;
	int needmore;
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);

	rnp->need_future_gp[c & 0x1] = 0;
	needmore = rnp->need_future_gp[(c + 1) & 0x1];
	trace_rcu_future_gp(rnp, rdp, c,
			    needmore ? TPS("CleanupMore") : TPS("Cleanup"));
	return needmore;
}

/*
 * Awaken the grace-period kthread for the specified flavor of RCU.
 * Don't do a self-awaken, and don't bother awakening when there is
 * nothing for the grace-period kthread to do (as in several CPUs
 * raced to awaken, and we lost), and finally don't try to awaken
 * a kthread that has not yet been created.
 */
static void rcu_gp_kthread_wake(struct rcu_state *rsp)
{
	if (current == rsp->gp_kthread ||
	    !READ_ONCE(rsp->gp_flags) ||
	    !rsp->gp_kthread)
		return;
	swake_up(&rsp->gp_wq);
}

/*
 * If there is room, assign a ->completed number to any callbacks on
 * this CPU that have not already been assigned.  Also accelerate any
 * callbacks that were previously assigned a ->completed number that has
 * since proven to be too conservative, which can happen if callbacks get
 * assigned a ->completed number while RCU is idle, but with reference to
 * a non-root rcu_node structure.  This function is idempotent, so it does
 * not hurt to call it repeatedly.  Returns an flag saying that we should
 * awaken the RCU grace-period kthread.
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
			       struct rcu_data *rdp)
{
	unsigned long c;
	int i;
	bool ret;

	/* If the CPU has no callbacks, nothing to do. */
	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
		return false;

	/*
	 * Starting from the sublist containing the callbacks most
	 * recently assigned a ->completed number and working down, find the
	 * first sublist that is not assignable to an upcoming grace period.
	 * Such a sublist has something in it (first two tests) and has
	 * a ->completed number assigned that will complete sooner than
	 * the ->completed number for newly arrived callbacks (last test).
	 *
	 * The key point is that any later sublist can be assigned the
	 * same ->completed number as the newly arrived callbacks, which
	 * means that the callbacks in any of these later sublist can be
	 * grouped into a single sublist, whether or not they have already
	 * been assigned a ->completed number.
	 */
	c = rcu_cbs_completed(rsp, rnp);
	for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
		if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
		    !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
			break;

	/*
	 * If there are no sublist for unassigned callbacks, leave.
	 * At the same time, advance "i" one sublist, so that "i" will
	 * index into the sublist where all the remaining callbacks should
	 * be grouped into.
	 */
	if (++i >= RCU_NEXT_TAIL)
		return false;

	/*
	 * Assign all subsequent callbacks' ->completed number to the next
	 * full grace period and group them all in the sublist initially
	 * indexed by "i".
	 */
	for (; i <= RCU_NEXT_TAIL; i++) {
		rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
		rdp->nxtcompleted[i] = c;
	}
	/* Record any needed additional grace periods. */
	ret = rcu_start_future_gp(rnp, rdp, NULL);

	/* Trace depending on how much we were able to accelerate. */
	if (!*rdp->nxttail[RCU_WAIT_TAIL])
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
	else
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
	return ret;
}

/*
 * Move any callbacks whose grace period has completed to the
 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
 * sublist.  This function is idempotent, so it does not hurt to
 * invoke it repeatedly.  As long as it is not invoked -too- often...
 * Returns true if the RCU grace-period kthread needs to be awakened.
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
			    struct rcu_data *rdp)
{
	int i, j;

	/* If the CPU has no callbacks, nothing to do. */
	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
		return false;

	/*
	 * Find all callbacks whose ->completed numbers indicate that they
	 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
	 */
	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
		if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
			break;
		rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
	}
	/* Clean up any sublist tail pointers that were misordered above. */
	for (j = RCU_WAIT_TAIL; j < i; j++)
		rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];

	/* Copy down callbacks to fill in empty sublists. */
	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
		if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
			break;
		rdp->nxttail[j] = rdp->nxttail[i];
		rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
	}

	/* Classify any remaining callbacks. */
	return rcu_accelerate_cbs(rsp, rnp, rdp);
}

/*
 * Update CPU-local rcu_data state to record the beginnings and ends of
 * grace periods.  The caller must hold the ->lock of the leaf rcu_node
 * structure corresponding to the current CPU, and must have irqs disabled.
 * Returns true if the grace-period kthread needs to be awakened.
 */
static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
			      struct rcu_data *rdp)
{
	bool ret;
	bool need_gp;

	/* Handle the ends of any preceding grace periods first. */
	if (rdp->completed == rnp->completed &&
	    !unlikely(READ_ONCE(rdp->gpwrap))) {

		/* No grace period end, so just accelerate recent callbacks. */
		ret = rcu_accelerate_cbs(rsp, rnp, rdp);

	} else {

		/* Advance callbacks. */
		ret = rcu_advance_cbs(rsp, rnp, rdp);

		/* Remember that we saw this grace-period completion. */
		rdp->completed = rnp->completed;
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
	}

	if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
		/*
		 * If the current grace period is waiting for this CPU,
		 * set up to detect a quiescent state, otherwise don't
		 * go looking for one.
		 */
		rdp->gpnum = rnp->gpnum;
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
		need_gp = !!(rnp->qsmask & rdp->grpmask);
		rdp->cpu_no_qs.b.norm = need_gp;
		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
		rdp->core_needs_qs = need_gp;
		zero_cpu_stall_ticks(rdp);
		WRITE_ONCE(rdp->gpwrap, false);
	}
	return ret;
}

static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
{
	unsigned long flags;
	bool needwake;
	struct rcu_node *rnp;

	local_irq_save(flags);
	rnp = rdp->mynode;
	if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
	     rdp->completed == READ_ONCE(rnp->completed) &&
	     !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
	    !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
		local_irq_restore(flags);
		return;
	}
	needwake = __note_gp_changes(rsp, rnp, rdp);
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
	if (needwake)
		rcu_gp_kthread_wake(rsp);
}

static void rcu_gp_slow(struct rcu_state *rsp, int delay)
{
	if (delay > 0 &&
	    !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
		schedule_timeout_uninterruptible(delay);
}

/*
 * Initialize a new grace period.  Return false if no grace period required.
 */
static bool rcu_gp_init(struct rcu_state *rsp)
{
	unsigned long oldmask;
	struct rcu_data *rdp;
	struct rcu_node *rnp = rcu_get_root(rsp);

	WRITE_ONCE(rsp->gp_activity, jiffies);
	raw_spin_lock_irq_rcu_node(rnp);
	if (!READ_ONCE(rsp->gp_flags)) {
		/* Spurious wakeup, tell caller to go back to sleep.  */
		raw_spin_unlock_irq_rcu_node(rnp);
		return false;
	}
	WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */

	if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
		/*
		 * Grace period already in progress, don't start another.
		 * Not supposed to be able to happen.
		 */
		raw_spin_unlock_irq_rcu_node(rnp);
		return false;
	}

	/* Advance to a new grace period and initialize state. */
	record_gp_stall_check_time(rsp);
	/* Record GP times before starting GP, hence smp_store_release(). */
	smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
	trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
	raw_spin_unlock_irq_rcu_node(rnp);

	/*
	 * Apply per-leaf buffered online and offline operations to the
	 * rcu_node tree.  Note that this new grace period need not wait
	 * for subsequent online CPUs, and that quiescent-state forcing
	 * will handle subsequent offline CPUs.
	 */
	rcu_for_each_leaf_node(rsp, rnp) {
		rcu_gp_slow(rsp, gp_preinit_delay);
		raw_spin_lock_irq_rcu_node(rnp);
		if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
		    !rnp->wait_blkd_tasks) {
			/* Nothing to do on this leaf rcu_node structure. */
			raw_spin_unlock_irq_rcu_node(rnp);
			continue;
		}

		/* Record old state, apply changes to ->qsmaskinit field. */
		oldmask = rnp->qsmaskinit;
		rnp->qsmaskinit = rnp->qsmaskinitnext;

		/* If zero-ness of ->qsmaskinit changed, propagate up tree. */
		if (!oldmask != !rnp->qsmaskinit) {
			if (!oldmask) /* First online CPU for this rcu_node. */
				rcu_init_new_rnp(rnp);
			else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
				rnp->wait_blkd_tasks = true;
			else /* Last offline CPU and can propagate. */
				rcu_cleanup_dead_rnp(rnp);
		}

		/*
		 * If all waited-on tasks from prior grace period are
		 * done, and if all this rcu_node structure's CPUs are
		 * still offline, propagate up the rcu_node tree and
		 * clear ->wait_blkd_tasks.  Otherwise, if one of this
		 * rcu_node structure's CPUs has since come back online,
		 * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
		 * checks for this, so just call it unconditionally).
		 */
		if (rnp->wait_blkd_tasks &&
		    (!rcu_preempt_has_tasks(rnp) ||
		     rnp->qsmaskinit)) {
			rnp->wait_blkd_tasks = false;
			rcu_cleanup_dead_rnp(rnp);
		}

		raw_spin_unlock_irq_rcu_node(rnp);
	}

	/*
	 * Set the quiescent-state-needed bits in all the rcu_node
	 * structures for all currently online CPUs in breadth-first order,
	 * starting from the root rcu_node structure, relying on the layout
	 * of the tree within the rsp->node[] array.  Note that other CPUs
	 * will access only the leaves of the hierarchy, thus seeing that no
	 * grace period is in progress, at least until the corresponding
	 * leaf node has been initialized.
	 *
	 * The grace period cannot complete until the initialization
	 * process finishes, because this kthread handles both.
	 */
	rcu_for_each_node_breadth_first(rsp, rnp) {
		rcu_gp_slow(rsp, gp_init_delay);
		raw_spin_lock_irq_rcu_node(rnp);
		rdp = this_cpu_ptr(rsp->rda);
		rcu_preempt_check_blocked_tasks(rnp);
		rnp->qsmask = rnp->qsmaskinit;
		WRITE_ONCE(rnp->gpnum, rsp->gpnum);
		if (WARN_ON_ONCE(rnp->completed != rsp->completed))
			WRITE_ONCE(rnp->completed, rsp->completed);
		if (rnp == rdp->mynode)
			(void)__note_gp_changes(rsp, rnp, rdp);
		rcu_preempt_boost_start_gp(rnp);
		trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
					    rnp->level, rnp->grplo,
					    rnp->grphi, rnp->qsmask);
		raw_spin_unlock_irq_rcu_node(rnp);
		cond_resched_rcu_qs();
		WRITE_ONCE(rsp->gp_activity, jiffies);
	}

	return true;
}

/*
 * Helper function for wait_event_interruptible_timeout() wakeup
 * at force-quiescent-state time.
 */
static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
{
	struct rcu_node *rnp = rcu_get_root(rsp);

	/* Someone like call_rcu() requested a force-quiescent-state scan. */
	*gfp = READ_ONCE(rsp->gp_flags);
	if (*gfp & RCU_GP_FLAG_FQS)
		return true;

	/* The current grace period has completed. */
	if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
		return true;

	return false;
}

/*
 * Do one round of quiescent-state forcing.
 */
static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
{
	bool isidle = false;
	unsigned long maxj;
	struct rcu_node *rnp = rcu_get_root(rsp);

	WRITE_ONCE(rsp->gp_activity, jiffies);
	rsp->n_force_qs++;
	if (first_time) {
		/* Collect dyntick-idle snapshots. */
		if (is_sysidle_rcu_state(rsp)) {
			isidle = true;
			maxj = jiffies - ULONG_MAX / 4;
		}
		force_qs_rnp(rsp, dyntick_save_progress_counter,
			     &isidle, &maxj);
		rcu_sysidle_report_gp(rsp, isidle, maxj);
	} else {
		/* Handle dyntick-idle and offline CPUs. */
		isidle = true;
		force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
	}
	/* Clear flag to prevent immediate re-entry. */
	if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
		raw_spin_lock_irq_rcu_node(rnp);
		WRITE_ONCE(rsp->gp_flags,
			   READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
		raw_spin_unlock_irq_rcu_node(rnp);
	}
}

/*
 * Clean up after the old grace period.
 */
static void rcu_gp_cleanup(struct rcu_state *rsp)
{
	unsigned long gp_duration;
	bool needgp = false;
	int nocb = 0;
	struct rcu_data *rdp;
	struct rcu_node *rnp = rcu_get_root(rsp);
	struct swait_queue_head *sq;

	WRITE_ONCE(rsp->gp_activity, jiffies);
	raw_spin_lock_irq_rcu_node(rnp);
	gp_duration = jiffies - rsp->gp_start;
	if (gp_duration > rsp->gp_max)
		rsp->gp_max = gp_duration;

	/*
	 * We know the grace period is complete, but to everyone else
	 * it appears to still be ongoing.  But it is also the case
	 * that to everyone else it looks like there is nothing that
	 * they can do to advance the grace period.  It is therefore
	 * safe for us to drop the lock in order to mark the grace
	 * period as completed in all of the rcu_node structures.
	 */
	raw_spin_unlock_irq_rcu_node(rnp);

	/*
	 * Propagate new ->completed value to rcu_node structures so
	 * that other CPUs don't have to wait until the start of the next
	 * grace period to process their callbacks.  This also avoids
	 * some nasty RCU grace-period initialization races by forcing
	 * the end of the current grace period to be completely recorded in
	 * all of the rcu_node structures before the beginning of the next
	 * grace period is recorded in any of the rcu_node structures.
	 */
	rcu_for_each_node_breadth_first(rsp, rnp) {
		raw_spin_lock_irq_rcu_node(rnp);
		WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
		WARN_ON_ONCE(rnp->qsmask);
		WRITE_ONCE(rnp->completed, rsp->gpnum);
		rdp = this_cpu_ptr(rsp->rda);
		if (rnp == rdp->mynode)
			needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
		/* smp_mb() provided by prior unlock-lock pair. */
		nocb += rcu_future_gp_cleanup(rsp, rnp);
		sq = rcu_nocb_gp_get(rnp);
		raw_spin_unlock_irq_rcu_node(rnp);
		rcu_nocb_gp_cleanup(sq);
		cond_resched_rcu_qs();
		WRITE_ONCE(rsp->gp_activity, jiffies);
		rcu_gp_slow(rsp, gp_cleanup_delay);
	}
	rnp = rcu_get_root(rsp);
	raw_spin_lock_irq_rcu_node(rnp); /* Order GP before ->completed update. */
	rcu_nocb_gp_set(rnp, nocb);

	/* Declare grace period done. */
	WRITE_ONCE(rsp->completed, rsp->gpnum);
	trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
	rsp->gp_state = RCU_GP_IDLE;
	rdp = this_cpu_ptr(rsp->rda);
	/* Advance CBs to reduce false positives below. */
	needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
	if (needgp || cpu_needs_another_gp(rsp, rdp)) {
		WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
		trace_rcu_grace_period(rsp->name,
				       READ_ONCE(rsp->gpnum),
				       TPS("newreq"));
	}
	raw_spin_unlock_irq_rcu_node(rnp);
}

/*
 * Body of kthread that handles grace periods.
 */
static int __noreturn rcu_gp_kthread(void *arg)
{
	bool first_gp_fqs;
	int gf;
	unsigned long j;
	int ret;
	struct rcu_state *rsp = arg;
	struct rcu_node *rnp = rcu_get_root(rsp);

	rcu_bind_gp_kthread();
	for (;;) {

		/* Handle grace-period start. */
		for (;;) {
			trace_rcu_grace_period(rsp->name,
					       READ_ONCE(rsp->gpnum),
					       TPS("reqwait"));
			rsp->gp_state = RCU_GP_WAIT_GPS;
			swait_event_interruptible(rsp->gp_wq,
						 READ_ONCE(rsp->gp_flags) &
						 RCU_GP_FLAG_INIT);
			rsp->gp_state = RCU_GP_DONE_GPS;
			/* Locking provides needed memory barrier. */
			if (rcu_gp_init(rsp))
				break;
			cond_resched_rcu_qs();
			WRITE_ONCE(rsp->gp_activity, jiffies);
			WARN_ON(signal_pending(current));
			trace_rcu_grace_period(rsp->name,
					       READ_ONCE(rsp->gpnum),
					       TPS("reqwaitsig"));
		}

		/* Handle quiescent-state forcing. */
		first_gp_fqs = true;
		j = jiffies_till_first_fqs;
		if (j > HZ) {
			j = HZ;
			jiffies_till_first_fqs = HZ;
		}
		ret = 0;
		for (;;) {
			if (!ret) {
				rsp->jiffies_force_qs = jiffies + j;
				WRITE_ONCE(rsp->jiffies_kick_kthreads,
					   jiffies + 3 * j);
			}
			trace_rcu_grace_period(rsp->name,
					       READ_ONCE(rsp->gpnum),
					       TPS("fqswait"));
			rsp->gp_state = RCU_GP_WAIT_FQS;
			ret = swait_event_interruptible_timeout(rsp->gp_wq,
					rcu_gp_fqs_check_wake(rsp, &gf), j);
			rsp->gp_state = RCU_GP_DOING_FQS;
			/* Locking provides needed memory barriers. */
			/* If grace period done, leave loop. */
			if (!READ_ONCE(rnp->qsmask) &&
			    !rcu_preempt_blocked_readers_cgp(rnp))
				break;
			/* If time for quiescent-state forcing, do it. */
			if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
			    (gf & RCU_GP_FLAG_FQS)) {
				trace_rcu_grace_period(rsp->name,
						       READ_ONCE(rsp->gpnum),
						       TPS("fqsstart"));
				rcu_gp_fqs(rsp, first_gp_fqs);
				first_gp_fqs = false;
				trace_rcu_grace_period(rsp->name,
						       READ_ONCE(rsp->gpnum),
						       TPS("fqsend"));
				cond_resched_rcu_qs();
				WRITE_ONCE(rsp->gp_activity, jiffies);
				ret = 0; /* Force full wait till next FQS. */
				j = jiffies_till_next_fqs;
				if (j > HZ) {
					j = HZ;
					jiffies_till_next_fqs = HZ;
				} else if (j < 1) {
					j = 1;
					jiffies_till_next_fqs = 1;
				}
			} else {
				/* Deal with stray signal. */
				cond_resched_rcu_qs();
				WRITE_ONCE(rsp->gp_activity, jiffies);
				WARN_ON(signal_pending(current));
				trace_rcu_grace_period(rsp->name,
						       READ_ONCE(rsp->gpnum),
						       TPS("fqswaitsig"));
				ret = 1; /* Keep old FQS timing. */
				j = jiffies;
				if (time_after(jiffies, rsp->jiffies_force_qs))
					j = 1;
				else
					j = rsp->jiffies_force_qs - j;
			}
		}

		/* Handle grace-period end. */
		rsp->gp_state = RCU_GP_CLEANUP;
		rcu_gp_cleanup(rsp);
		rsp->gp_state = RCU_GP_CLEANED;
	}
}

/*
 * Start a new RCU grace period if warranted, re-initializing the hierarchy
 * in preparation for detecting the next grace period.  The caller must hold
 * the root node's ->lock and hard irqs must be disabled.
 *
 * Note that it is legal for a dying CPU (which is marked as offline) to
 * invoke this function.  This can happen when the dying CPU reports its
 * quiescent state.
 *
 * Returns true if the grace-period kthread must be awakened.
 */
static bool
rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
		      struct rcu_data *rdp)
{
	if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
		/*
		 * Either we have not yet spawned the grace-period
		 * task, this CPU does not need another grace period,
		 * or a grace period is already in progress.
		 * Either way, don't start a new grace period.
		 */
		return false;
	}
	WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
	trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
			       TPS("newreq"));

	/*
	 * We can't do wakeups while holding the rnp->lock, as that
	 * could cause possible deadlocks with the rq->lock. Defer
	 * the wakeup to our caller.
	 */
	return true;
}

/*
 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
 * callbacks.  Note that rcu_start_gp_advanced() cannot do this because it
 * is invoked indirectly from rcu_advance_cbs(), which would result in
 * endless recursion -- or would do so if it wasn't for the self-deadlock
 * that is encountered beforehand.
 *
 * Returns true if the grace-period kthread needs to be awakened.
 */
static bool rcu_start_gp(struct rcu_state *rsp)
{
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
	struct rcu_node *rnp = rcu_get_root(rsp);
	bool ret = false;

	/*
	 * If there is no grace period in progress right now, any
	 * callbacks we have up to this point will be satisfied by the
	 * next grace period.  Also, advancing the callbacks reduces the
	 * probability of false positives from cpu_needs_another_gp()
	 * resulting in pointless grace periods.  So, advance callbacks
	 * then start the grace period!
	 */
	ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
	ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
	return ret;
}

/*
 * Report a full set of quiescent states to the specified rcu_state data
 * structure.  Invoke rcu_gp_kthread_wake() to awaken the grace-period
 * kthread if another grace period is required.  Whether we wake
 * the grace-period kthread or it awakens itself for the next round
 * of quiescent-state forcing, that kthread will clean up after the
 * just-completed grace period.  Note that the caller must hold rnp->lock,
 * which is released before return.
 */
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
	__releases(rcu_get_root(rsp)->lock)
{
	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
	WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
	raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
	rcu_gp_kthread_wake(rsp);
}

/*
 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
 * Allows quiescent states for a group of CPUs to be reported at one go
 * to the specified rcu_node structure, though all the CPUs in the group
 * must be represented by the same rcu_node structure (which need not be a
 * leaf rcu_node structure, though it often will be).  The gps parameter
 * is the grace-period snapshot, which means that the quiescent states
 * are valid only if rnp->gpnum is equal to gps.  That structure's lock
 * must be held upon entry, and it is released before return.
 */
static void
rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
		  struct rcu_node *rnp, unsigned long gps, unsigned long flags)
	__releases(rnp->lock)
{
	unsigned long oldmask = 0;
	struct rcu_node *rnp_c;

	/* Walk up the rcu_node hierarchy. */
	for (;;) {
		if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {

			/*
			 * Our bit has already been cleared, or the
			 * relevant grace period is already over, so done.
			 */
			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
			return;
		}
		WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
		rnp->qsmask &= ~mask;
		trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
						 mask, rnp->qsmask, rnp->level,
						 rnp->grplo, rnp->grphi,
						 !!rnp->gp_tasks);
		if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {

			/* Other bits still set at this level, so done. */
			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
			return;
		}
		mask = rnp->grpmask;
		if (rnp->parent == NULL) {

			/* No more levels.  Exit loop holding root lock. */

			break;
		}
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		rnp_c = rnp;
		rnp = rnp->parent;
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		oldmask = rnp_c->qsmask;
	}

	/*
	 * Get here if we are the last CPU to pass through a quiescent
	 * state for this grace period.  Invoke rcu_report_qs_rsp()
	 * to clean up and start the next grace period if one is needed.
	 */
	rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
}

/*
 * Record a quiescent state for all tasks that were previously queued
 * on the specified rcu_node structure and that were blocking the current
 * RCU grace period.  The caller must hold the specified rnp->lock with
 * irqs disabled, and this lock is released upon return, but irqs remain
 * disabled.
 */
static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
				      struct rcu_node *rnp, unsigned long flags)
	__releases(rnp->lock)
{
	unsigned long gps;
	unsigned long mask;
	struct rcu_node *rnp_p;

	if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
	    rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		return;  /* Still need more quiescent states! */
	}

	rnp_p = rnp->parent;
	if (rnp_p == NULL) {
		/*
		 * Only one rcu_node structure in the tree, so don't
		 * try to report up to its nonexistent parent!
		 */
		rcu_report_qs_rsp(rsp, flags);
		return;
	}

	/* Report up the rest of the hierarchy, tracking current ->gpnum. */
	gps = rnp->gpnum;
	mask = rnp->grpmask;
	raw_spin_unlock_rcu_node(rnp);	/* irqs remain disabled. */
	raw_spin_lock_rcu_node(rnp_p);	/* irqs already disabled. */
	rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
}

/*
 * Record a quiescent state for the specified CPU to that CPU's rcu_data
 * structure.  This must be called from the specified CPU.
 */
static void
rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
{
	unsigned long flags;
	unsigned long mask;
	bool needwake;
	struct rcu_node *rnp;

	rnp = rdp->mynode;
	raw_spin_lock_irqsave_rcu_node(rnp, flags);
	if (rdp->cpu_no_qs.b.norm || rdp->gpnum != rnp->gpnum ||
	    rnp->completed == rnp->gpnum || rdp->gpwrap) {

		/*
		 * The grace period in which this quiescent state was
		 * recorded has ended, so don't report it upwards.
		 * We will instead need a new quiescent state that lies
		 * within the current grace period.
		 */
		rdp->cpu_no_qs.b.norm = true;	/* need qs for new gp. */
		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		return;
	}
	mask = rdp->grpmask;
	if ((rnp->qsmask & mask) == 0) {
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
	} else {
		rdp->core_needs_qs = false;

		/*
		 * This GP can't end until cpu checks in, so all of our
		 * callbacks can be processed during the next GP.
		 */
		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);

		rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
		/* ^^^ Released rnp->lock */
		if (needwake)
			rcu_gp_kthread_wake(rsp);
	}
}

/*
 * Check to see if there is a new grace period of which this CPU
 * is not yet aware, and if so, set up local rcu_data state for it.
 * Otherwise, see if this CPU has just passed through its first
 * quiescent state for this grace period, and record that fact if so.
 */
static void
rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
{
	/* Check for grace-period ends and beginnings. */
	note_gp_changes(rsp, rdp);

	/*
	 * Does this CPU still need to do its part for current grace period?
	 * If no, return and let the other CPUs do their part as well.
	 */
	if (!rdp->core_needs_qs)
		return;

	/*
	 * Was there a quiescent state since the beginning of the grace
	 * period? If no, then exit and wait for the next call.
	 */
	if (rdp->cpu_no_qs.b.norm)
		return;

	/*
	 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
	 * judge of that).
	 */
	rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
}

/*
 * Send the specified CPU's RCU callbacks to the orphanage.  The
 * specified CPU must be offline, and the caller must hold the
 * ->orphan_lock.
 */
static void
rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
			  struct rcu_node *rnp, struct rcu_data *rdp)
{
	/* No-CBs CPUs do not have orphanable callbacks. */
	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu))
		return;

	/*
	 * Orphan the callbacks.  First adjust the counts.  This is safe
	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
	 * cannot be running now.  Thus no memory barrier is required.
	 */
	if (rdp->nxtlist != NULL) {
		rsp->qlen_lazy += rdp->qlen_lazy;
		rsp->qlen += rdp->qlen;
		rdp->n_cbs_orphaned += rdp->qlen;
		rdp->qlen_lazy = 0;
		WRITE_ONCE(rdp->qlen, 0);
	}

	/*
	 * Next, move those callbacks still needing a grace period to
	 * the orphanage, where some other CPU will pick them up.
	 * Some of the callbacks might have gone partway through a grace
	 * period, but that is too bad.  They get to start over because we
	 * cannot assume that grace periods are synchronized across CPUs.
	 * We don't bother updating the ->nxttail[] array yet, instead
	 * we just reset the whole thing later on.
	 */
	if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
		*rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
		rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
		*rdp->nxttail[RCU_DONE_TAIL] = NULL;
	}

	/*
	 * Then move the ready-to-invoke callbacks to the orphanage,
	 * where some other CPU will pick them up.  These will not be
	 * required to pass though another grace period: They are done.
	 */
	if (rdp->nxtlist != NULL) {
		*rsp->orphan_donetail = rdp->nxtlist;
		rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
	}

	/*
	 * Finally, initialize the rcu_data structure's list to empty and
	 * disallow further callbacks on this CPU.
	 */
	init_callback_list(rdp);
	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
}

/*
 * Adopt the RCU callbacks from the specified rcu_state structure's
 * orphanage.  The caller must hold the ->orphan_lock.
 */
static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
{
	int i;
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);

	/* No-CBs CPUs are handled specially. */
	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
	    rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
		return;

	/* Do the accounting first. */
	rdp->qlen_lazy += rsp->qlen_lazy;
	rdp->qlen += rsp->qlen;
	rdp->n_cbs_adopted += rsp->qlen;
	if (rsp->qlen_lazy != rsp->qlen)
		rcu_idle_count_callbacks_posted();
	rsp->qlen_lazy = 0;
	rsp->qlen = 0;

	/*
	 * We do not need a memory barrier here because the only way we
	 * can get here if there is an rcu_barrier() in flight is if
	 * we are the task doing the rcu_barrier().
	 */

	/* First adopt the ready-to-invoke callbacks. */
	if (rsp->orphan_donelist != NULL) {
		*rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
		*rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
		for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
			if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
				rdp->nxttail[i] = rsp->orphan_donetail;
		rsp->orphan_donelist = NULL;
		rsp->orphan_donetail = &rsp->orphan_donelist;
	}

	/* And then adopt the callbacks that still need a grace period. */
	if (rsp->orphan_nxtlist != NULL) {
		*rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
		rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
		rsp->orphan_nxtlist = NULL;
		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
	}
}

/*
 * Trace the fact that this CPU is going offline.
 */
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
	RCU_TRACE(unsigned long mask);
	RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
	RCU_TRACE(struct rcu_node *rnp = rdp->mynode);

	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
		return;

	RCU_TRACE(mask = rdp->grpmask);
	trace_rcu_grace_period(rsp->name,
			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
			       TPS("cpuofl"));
}

/*
 * All CPUs for the specified rcu_node structure have gone offline,
 * and all tasks that were preempted within an RCU read-side critical
 * section while running on one of those CPUs have since exited their RCU
 * read-side critical section.  Some other CPU is reporting this fact with
 * the specified rcu_node structure's ->lock held and interrupts disabled.
 * This function therefore goes up the tree of rcu_node structures,
 * clearing the corresponding bits in the ->qsmaskinit fields.  Note that
 * the leaf rcu_node structure's ->qsmaskinit field has already been
 * updated
 *
 * This function does check that the specified rcu_node structure has
 * all CPUs offline and no blocked tasks, so it is OK to invoke it
 * prematurely.  That said, invoking it after the fact will cost you
 * a needless lock acquisition.  So once it has done its work, don't
 * invoke it again.
 */
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
{
	long mask;
	struct rcu_node *rnp = rnp_leaf;

	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
	    rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
		return;
	for (;;) {
		mask = rnp->grpmask;
		rnp = rnp->parent;
		if (!rnp)
			break;
		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
		rnp->qsmaskinit &= ~mask;
		rnp->qsmask &= ~mask;
		if (rnp->qsmaskinit) {
			raw_spin_unlock_rcu_node(rnp);
			/* irqs remain disabled. */
			return;
		}
		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
	}
}

/*
 * The CPU has been completely removed, and some other CPU is reporting
 * this fact from process context.  Do the remainder of the cleanup,
 * including orphaning the outgoing CPU's RCU callbacks, and also
 * adopting them.  There can only be one CPU hotplug operation at a time,
 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
 */
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
	unsigned long flags;
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */

	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
		return;

	/* Adjust any no-longer-needed kthreads. */
	rcu_boost_kthread_setaffinity(rnp, -1);

	/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
	raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
	rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
	rcu_adopt_orphan_cbs(rsp, flags);
	raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);

	WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
		  cpu, rdp->qlen, rdp->nxtlist);
}

/*
 * Invoke any RCU callbacks that have made it to the end of their grace
 * period.  Thottle as specified by rdp->blimit.
 */
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
	unsigned long flags;
	struct rcu_head *next, *list, **tail;
	long bl, count, count_lazy;
	int i;

	/* If no callbacks are ready, just return. */
	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
		trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
		trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist),
				    need_resched(), is_idle_task(current),
				    rcu_is_callbacks_kthread());
		return;
	}

	/*
	 * Extract the list of ready callbacks, disabling to prevent
	 * races with call_rcu() from interrupt handlers.
	 */
	local_irq_save(flags);
	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
	bl = rdp->blimit;
	trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
	list = rdp->nxtlist;
	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
	tail = rdp->nxttail[RCU_DONE_TAIL];
	for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
		if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
			rdp->nxttail[i] = &rdp->nxtlist;
	local_irq_restore(flags);

	/* Invoke callbacks. */
	count = count_lazy = 0;
	while (list) {
		next = list->next;
		prefetch(next);
		debug_rcu_head_unqueue(list);
		if (__rcu_reclaim(rsp->name, list))
			count_lazy++;
		list = next;
		/* Stop only if limit reached and CPU has something to do. */
		if (++count >= bl &&
		    (need_resched() ||
		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
			break;
	}

	local_irq_save(flags);
	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
			    is_idle_task(current),
			    rcu_is_callbacks_kthread());

	/* Update count, and requeue any remaining callbacks. */
	if (list != NULL) {
		*tail = rdp->nxtlist;
		rdp->nxtlist = list;
		for (i = 0; i < RCU_NEXT_SIZE; i++)
			if (&rdp->nxtlist == rdp->nxttail[i])
				rdp->nxttail[i] = tail;
			else
				break;
	}
	smp_mb(); /* List handling before counting for rcu_barrier(). */
	rdp->qlen_lazy -= count_lazy;
	WRITE_ONCE(rdp->qlen, rdp->qlen - count);
	rdp->n_cbs_invoked += count;

	/* Reinstate batch limit if we have worked down the excess. */
	if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
		rdp->blimit = blimit;

	/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
	if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
		rdp->qlen_last_fqs_check = 0;
		rdp->n_force_qs_snap = rsp->n_force_qs;
	} else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
		rdp->qlen_last_fqs_check = rdp->qlen;
	WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));

	local_irq_restore(flags);

	/* Re-invoke RCU core processing if there are callbacks remaining. */
	if (cpu_has_callbacks_ready_to_invoke(rdp))
		invoke_rcu_core();
}

/*
 * Check to see if this CPU is in a non-context-switch quiescent state
 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
 * Also schedule RCU core processing.
 *
 * This function must be called from hardirq context.  It is normally
 * invoked from the scheduling-clock interrupt.
 */
void rcu_check_callbacks(int user)
{
	trace_rcu_utilization(TPS("Start scheduler-tick"));
	increment_cpu_stall_ticks();
	if (user || rcu_is_cpu_rrupt_from_idle()) {

		/*
		 * Get here if this CPU took its interrupt from user
		 * mode or from the idle loop, and if this is not a
		 * nested interrupt.  In this case, the CPU is in
		 * a quiescent state, so note it.
		 *
		 * No memory barrier is required here because both
		 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
		 * variables that other CPUs neither access nor modify,
		 * at least not while the corresponding CPU is online.
		 */

		rcu_sched_qs();
		rcu_bh_qs();

	} else if (!in_softirq()) {

		/*
		 * Get here if this CPU did not take its interrupt from
		 * softirq, in other words, if it is not interrupting
		 * a rcu_bh read-side critical section.  This is an _bh
		 * critical section, so note it.
		 */

		rcu_bh_qs();
	}
	rcu_preempt_check_callbacks();
	if (rcu_pending())
		invoke_rcu_core();
	if (user)
		rcu_note_voluntary_context_switch(current);
	trace_rcu_utilization(TPS("End scheduler-tick"));
}

/*
 * Scan the leaf rcu_node structures, processing dyntick state for any that
 * have not yet encountered a quiescent state, using the function specified.
 * Also initiate boosting for any threads blocked on the root rcu_node.
 *
 * The caller must have suppressed start of new grace periods.
 */
static void force_qs_rnp(struct rcu_state *rsp,
			 int (*f)(struct rcu_data *rsp, bool *isidle,
				  unsigned long *maxj),
			 bool *isidle, unsigned long *maxj)
{
	int cpu;
	unsigned long flags;
	unsigned long mask;
	struct rcu_node *rnp;

	rcu_for_each_leaf_node(rsp, rnp) {
		cond_resched_rcu_qs();
		mask = 0;
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		if (rnp->qsmask == 0) {
			if (rcu_state_p == &rcu_sched_state ||
			    rsp != rcu_state_p ||
			    rcu_preempt_blocked_readers_cgp(rnp)) {
				/*
				 * No point in scanning bits because they
				 * are all zero.  But we might need to
				 * priority-boost blocked readers.
				 */
				rcu_initiate_boost(rnp, flags);
				/* rcu_initiate_boost() releases rnp->lock */
				continue;
			}
			if (rnp->parent &&
			    (rnp->parent->qsmask & rnp->grpmask)) {
				/*
				 * Race between grace-period
				 * initialization and task exiting RCU
				 * read-side critical section: Report.
				 */
				rcu_report_unblock_qs_rnp(rsp, rnp, flags);
				/* rcu_report_unblock_qs_rnp() rlses ->lock */
				continue;
			}
		}
		for_each_leaf_node_possible_cpu(rnp, cpu) {
			unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
			if ((rnp->qsmask & bit) != 0) {
				if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
					mask |= bit;
			}
		}
		if (mask != 0) {
			/* Idle/offline CPUs, report (releases rnp->lock. */
			rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
		} else {
			/* Nothing to do here, so just drop the lock. */
			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		}
	}
}

/*
 * Force quiescent states on reluctant CPUs, and also detect which
 * CPUs are in dyntick-idle mode.
 */
static void force_quiescent_state(struct rcu_state *rsp)
{
	unsigned long flags;
	bool ret;
	struct rcu_node *rnp;
	struct rcu_node *rnp_old = NULL;

	/* Funnel through hierarchy to reduce memory contention. */
	rnp = __this_cpu_read(rsp->rda->mynode);
	for (; rnp != NULL; rnp = rnp->parent) {
		ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
		      !raw_spin_trylock(&rnp->fqslock);
		if (rnp_old != NULL)
			raw_spin_unlock(&rnp_old->fqslock);
		if (ret) {
			rsp->n_force_qs_lh++;
			return;
		}
		rnp_old = rnp;
	}
	/* rnp_old == rcu_get_root(rsp), rnp == NULL. */

	/* Reached the root of the rcu_node tree, acquire lock. */
	raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
	raw_spin_unlock(&rnp_old->fqslock);
	if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
		rsp->n_force_qs_lh++;
		raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
		return;  /* Someone beat us to it. */
	}
	WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
	raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
	rcu_gp_kthread_wake(rsp);
}

/*
 * This does the RCU core processing work for the specified rcu_state
 * and rcu_data structures.  This may be called only from the CPU to
 * whom the rdp belongs.
 */
static void
__rcu_process_callbacks(struct rcu_state *rsp)
{
	unsigned long flags;
	bool needwake;
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);

	WARN_ON_ONCE(rdp->beenonline == 0);

	/* Update RCU state based on any recent quiescent states. */
	rcu_check_quiescent_state(rsp, rdp);

	/* Does this CPU require a not-yet-started grace period? */
	local_irq_save(flags);
	if (cpu_needs_another_gp(rsp, rdp)) {
		raw_spin_lock_rcu_node(rcu_get_root(rsp)); /* irqs disabled. */
		needwake = rcu_start_gp(rsp);
		raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
		if (needwake)
			rcu_gp_kthread_wake(rsp);
	} else {
		local_irq_restore(flags);
	}

	/* If there are callbacks ready, invoke them. */
	if (cpu_has_callbacks_ready_to_invoke(rdp))
		invoke_rcu_callbacks(rsp, rdp);

	/* Do any needed deferred wakeups of rcuo kthreads. */
	do_nocb_deferred_wakeup(rdp);
}

/*
 * Do RCU core processing for the current CPU.
 */
static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
{
	struct rcu_state *rsp;

	if (cpu_is_offline(smp_processor_id()))
		return;
	trace_rcu_utilization(TPS("Start RCU core"));
	for_each_rcu_flavor(rsp)
		__rcu_process_callbacks(rsp);
	trace_rcu_utilization(TPS("End RCU core"));
}

/*
 * Schedule RCU callback invocation.  If the specified type of RCU
 * does not support RCU priority boosting, just do a direct call,
 * otherwise wake up the per-CPU kernel kthread.  Note that because we
 * are running on the current CPU with softirqs disabled, the
 * rcu_cpu_kthread_task cannot disappear out from under us.
 */
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
{
	if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
		return;
	if (likely(!rsp->boost)) {
		rcu_do_batch(rsp, rdp);
		return;
	}
	invoke_rcu_callbacks_kthread();
}

static void invoke_rcu_core(void)
{
	if (cpu_online(smp_processor_id()))
		raise_softirq(RCU_SOFTIRQ);
}

/*
 * Handle any core-RCU processing required by a call_rcu() invocation.
 */
static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
			    struct rcu_head *head, unsigned long flags)
{
	bool needwake;

	/*
	 * If called from an extended quiescent state, invoke the RCU
	 * core in order to force a re-evaluation of RCU's idleness.
	 */
	if (!rcu_is_watching())
		invoke_rcu_core();

	/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
	if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
		return;

	/*
	 * Force the grace period if too many callbacks or too long waiting.
	 * Enforce hysteresis, and don't invoke force_quiescent_state()
	 * if some other CPU has recently done so.  Also, don't bother
	 * invoking force_quiescent_state() if the newly enqueued callback
	 * is the only one waiting for a grace period to complete.
	 */
	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {

		/* Are we ignoring a completed grace period? */
		note_gp_changes(rsp, rdp);

		/* Start a new grace period if one not already started. */
		if (!rcu_gp_in_progress(rsp)) {
			struct rcu_node *rnp_root = rcu_get_root(rsp);

			raw_spin_lock_rcu_node(rnp_root);
			needwake = rcu_start_gp(rsp);
			raw_spin_unlock_rcu_node(rnp_root);
			if (needwake)
				rcu_gp_kthread_wake(rsp);
		} else {
			/* Give the grace period a kick. */
			rdp->blimit = LONG_MAX;
			if (rsp->n_force_qs == rdp->n_force_qs_snap &&
			    *rdp->nxttail[RCU_DONE_TAIL] != head)
				force_quiescent_state(rsp);
			rdp->n_force_qs_snap = rsp->n_force_qs;
			rdp->qlen_last_fqs_check = rdp->qlen;
		}
	}
}

/*
 * RCU callback function to leak a callback.
 */
static void rcu_leak_callback(struct rcu_head *rhp)
{
}

/*
 * Helper function for call_rcu() and friends.  The cpu argument will
 * normally be -1, indicating "currently running CPU".  It may specify
 * a CPU only if that CPU is a no-CBs CPU.  Currently, only _rcu_barrier()
 * is expected to specify a CPU.
 */
static void
__call_rcu(struct rcu_head *head, rcu_callback_t func,
	   struct rcu_state *rsp, int cpu, bool lazy)
{
	unsigned long flags;
	struct rcu_data *rdp;

	/* Misaligned rcu_head! */
	WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));

	if (debug_rcu_head_queue(head)) {
		/* Probable double call_rcu(), so leak the callback. */
		WRITE_ONCE(head->func, rcu_leak_callback);
		WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
		return;
	}
	head->func = func;
	head->next = NULL;
	local_irq_save(flags);
	rdp = this_cpu_ptr(rsp->rda);

	/* Add the callback to our list. */
	if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
		int offline;

		if (cpu != -1)
			rdp = per_cpu_ptr(rsp->rda, cpu);
		if (likely(rdp->mynode)) {
			/* Post-boot, so this should be for a no-CBs CPU. */
			offline = !__call_rcu_nocb(rdp, head, lazy, flags);
			WARN_ON_ONCE(offline);
			/* Offline CPU, _call_rcu() illegal, leak callback.  */
			local_irq_restore(flags);
			return;
		}
		/*
		 * Very early boot, before rcu_init().  Initialize if needed
		 * and then drop through to queue the callback.
		 */
		BUG_ON(cpu != -1);
		WARN_ON_ONCE(!rcu_is_watching());
		if (!likely(rdp->nxtlist))
			init_default_callback_list(rdp);
	}
	WRITE_ONCE(rdp->qlen, rdp->qlen + 1);
	if (lazy)
		rdp->qlen_lazy++;
	else
		rcu_idle_count_callbacks_posted();
	smp_mb();  /* Count before adding callback for rcu_barrier(). */
	*rdp->nxttail[RCU_NEXT_TAIL] = head;
	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;

	if (__is_kfree_rcu_offset((unsigned long)func))
		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
					 rdp->qlen_lazy, rdp->qlen);
	else
		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);

	/* Go handle any RCU core processing required. */
	__call_rcu_core(rsp, rdp, head, flags);
	local_irq_restore(flags);
}

/*
 * Queue an RCU-sched callback for invocation after a grace period.
 */
void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
{
	__call_rcu(head, func, &rcu_sched_state, -1, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_sched);

/*
 * Queue an RCU callback for invocation after a quicker grace period.
 */
void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
{
	__call_rcu(head, func, &rcu_bh_state, -1, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);

/*
 * Queue an RCU callback for lazy invocation after a grace period.
 * This will likely be later named something like "call_rcu_lazy()",
 * but this change will require some way of tagging the lazy RCU
 * callbacks in the list of pending callbacks. Until then, this
 * function may only be called from __kfree_rcu().
 */
void kfree_call_rcu(struct rcu_head *head,
		    rcu_callback_t func)
{
	__call_rcu(head, func, rcu_state_p, -1, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

/*
 * Because a context switch is a grace period for RCU-sched and RCU-bh,
 * any blocking grace-period wait automatically implies a grace period
 * if there is only one CPU online at any point time during execution
 * of either synchronize_sched() or synchronize_rcu_bh().  It is OK to
 * occasionally incorrectly indicate that there are multiple CPUs online
 * when there was in fact only one the whole time, as this just adds
 * some overhead: RCU still operates correctly.
 */
static inline int rcu_blocking_is_gp(void)
{
	int ret;

	might_sleep();  /* Check for RCU read-side critical section. */
	preempt_disable();
	ret = num_online_cpus() <= 1;
	preempt_enable();
	return ret;
}

/**
 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
 *
 * Control will return to the caller some time after a full rcu-sched
 * grace period has elapsed, in other words after all currently executing
 * rcu-sched read-side critical sections have completed.   These read-side
 * critical sections are delimited by rcu_read_lock_sched() and
 * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
 * local_irq_disable(), and so on may be used in place of
 * rcu_read_lock_sched().
 *
 * This means that all preempt_disable code sequences, including NMI and
 * non-threaded hardware-interrupt handlers, in progress on entry will
 * have completed before this primitive returns.  However, this does not
 * guarantee that softirq handlers will have completed, since in some
 * kernels, these handlers can run in process context, and can block.
 *
 * Note that this guarantee implies further memory-ordering guarantees.
 * On systems with more than one CPU, when synchronize_sched() returns,
 * each CPU is guaranteed to have executed a full memory barrier since the
 * end of its last RCU-sched read-side critical section whose beginning
 * preceded the call to synchronize_sched().  In addition, each CPU having
 * an RCU read-side critical section that extends beyond the return from
 * synchronize_sched() is guaranteed to have executed a full memory barrier
 * after the beginning of synchronize_sched() and before the beginning of
 * that RCU read-side critical section.  Note that these guarantees include
 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
 * that are executing in the kernel.
 *
 * Furthermore, if CPU A invoked synchronize_sched(), which returned
 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
 * to have executed a full memory barrier during the execution of
 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
 * again only if the system has more than one CPU).
 *
 * This primitive provides the guarantees made by the (now removed)
 * synchronize_kernel() API.  In contrast, synchronize_rcu() only
 * guarantees that rcu_read_lock() sections will have completed.
 * In "classic RCU", these two guarantees happen to be one and
 * the same, but can differ in realtime RCU implementations.
 */
void synchronize_sched(void)
{
	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
			 lock_is_held(&rcu_lock_map) ||
			 lock_is_held(&rcu_sched_lock_map),
			 "Illegal synchronize_sched() in RCU-sched read-side critical section");
	if (rcu_blocking_is_gp())
		return;
	if (rcu_gp_is_expedited())
		synchronize_sched_expedited();
	else
		wait_rcu_gp(call_rcu_sched);
}
EXPORT_SYMBOL_GPL(synchronize_sched);

/**
 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
 *
 * Control will return to the caller some time after a full rcu_bh grace
 * period has elapsed, in other words after all currently executing rcu_bh
 * read-side critical sections have completed.  RCU read-side critical
 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
 * and may be nested.
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
 */
void synchronize_rcu_bh(void)
{
	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
			 lock_is_held(&rcu_lock_map) ||
			 lock_is_held(&rcu_sched_lock_map),
			 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
	if (rcu_blocking_is_gp())
		return;
	if (rcu_gp_is_expedited())
		synchronize_rcu_bh_expedited();
	else
		wait_rcu_gp(call_rcu_bh);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);

/**
 * get_state_synchronize_rcu - Snapshot current RCU state
 *
 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
 * to determine whether or not a full grace period has elapsed in the
 * meantime.
 */
unsigned long get_state_synchronize_rcu(void)
{
	/*
	 * Any prior manipulation of RCU-protected data must happen
	 * before the load from ->gpnum.
	 */
	smp_mb();  /* ^^^ */

	/*
	 * Make sure this load happens before the purportedly
	 * time-consuming work between get_state_synchronize_rcu()
	 * and cond_synchronize_rcu().
	 */
	return smp_load_acquire(&rcu_state_p->gpnum);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);

/**
 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
 *
 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
 *
 * If a full RCU grace period has elapsed since the earlier call to
 * get_state_synchronize_rcu(), just return.  Otherwise, invoke
 * synchronize_rcu() to wait for a full grace period.
 *
 * Yes, this function does not take counter wrap into account.  But
 * counter wrap is harmless.  If the counter wraps, we have waited for
 * more than 2 billion grace periods (and way more on a 64-bit system!),
 * so waiting for one additional grace period should be just fine.
 */
void cond_synchronize_rcu(unsigned long oldstate)
{
	unsigned long newstate;

	/*
	 * Ensure that this load happens before any RCU-destructive
	 * actions the caller might carry out after we return.
	 */
	newstate = smp_load_acquire(&rcu_state_p->completed);
	if (ULONG_CMP_GE(oldstate, newstate))
		synchronize_rcu();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);

/**
 * get_state_synchronize_sched - Snapshot current RCU-sched state
 *
 * Returns a cookie that is used by a later call to cond_synchronize_sched()
 * to determine whether or not a full grace period has elapsed in the
 * meantime.
 */
unsigned long get_state_synchronize_sched(void)
{
	/*
	 * Any prior manipulation of RCU-protected data must happen
	 * before the load from ->gpnum.
	 */
	smp_mb();  /* ^^^ */

	/*
	 * Make sure this load happens before the purportedly
	 * time-consuming work between get_state_synchronize_sched()
	 * and cond_synchronize_sched().
	 */
	return smp_load_acquire(&rcu_sched_state.gpnum);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_sched);

/**
 * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
 *
 * @oldstate: return value from earlier call to get_state_synchronize_sched()
 *
 * If a full RCU-sched grace period has elapsed since the earlier call to
 * get_state_synchronize_sched(), just return.  Otherwise, invoke
 * synchronize_sched() to wait for a full grace period.
 *
 * Yes, this function does not take counter wrap into account.  But
 * counter wrap is harmless.  If the counter wraps, we have waited for
 * more than 2 billion grace periods (and way more on a 64-bit system!),
 * so waiting for one additional grace period should be just fine.
 */
void cond_synchronize_sched(unsigned long oldstate)
{
	unsigned long newstate;

	/*
	 * Ensure that this load happens before any RCU-destructive
	 * actions the caller might carry out after we return.
	 */
	newstate = smp_load_acquire(&rcu_sched_state.completed);
	if (ULONG_CMP_GE(oldstate, newstate))
		synchronize_sched();
}
EXPORT_SYMBOL_GPL(cond_synchronize_sched);

/* Adjust sequence number for start of update-side operation. */
static void rcu_seq_start(unsigned long *sp)
{
	WRITE_ONCE(*sp, *sp + 1);
	smp_mb(); /* Ensure update-side operation after counter increment. */
	WARN_ON_ONCE(!(*sp & 0x1));
}

/* Adjust sequence number for end of update-side operation. */
static void rcu_seq_end(unsigned long *sp)
{
	smp_mb(); /* Ensure update-side operation before counter increment. */
	WRITE_ONCE(*sp, *sp + 1);
	WARN_ON_ONCE(*sp & 0x1);
}

/* Take a snapshot of the update side's sequence number. */
static unsigned long rcu_seq_snap(unsigned long *sp)
{
	unsigned long s;

	s = (READ_ONCE(*sp) + 3) & ~0x1;
	smp_mb(); /* Above access must not bleed into critical section. */
	return s;
}

/*
 * Given a snapshot from rcu_seq_snap(), determine whether or not a
 * full update-side operation has occurred.
 */
static bool rcu_seq_done(unsigned long *sp, unsigned long s)
{
	return ULONG_CMP_GE(READ_ONCE(*sp), s);
}

/*
 * Check to see if there is any immediate RCU-related work to be done
 * by the current CPU, for the specified type of RCU, returning 1 if so.
 * The checks are in order of increasing expense: checks that can be
 * carried out against CPU-local state are performed first.  However,
 * we must check for CPU stalls first, else we might not get a chance.
 */
static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
{
	struct rcu_node *rnp = rdp->mynode;

	rdp->n_rcu_pending++;

	/* Check for CPU stalls, if enabled. */
	check_cpu_stall(rsp, rdp);

	/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
	if (rcu_nohz_full_cpu(rsp))
		return 0;

	/* Is the RCU core waiting for a quiescent state from this CPU? */
	if (rcu_scheduler_fully_active &&
	    rdp->core_needs_qs && rdp->cpu_no_qs.b.norm &&
	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
		rdp->n_rp_core_needs_qs++;
	} else if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm) {
		rdp->n_rp_report_qs++;
		return 1;
	}

	/* Does this CPU have callbacks ready to invoke? */
	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
		rdp->n_rp_cb_ready++;
		return 1;
	}

	/* Has RCU gone idle with this CPU needing another grace period? */
	if (cpu_needs_another_gp(rsp, rdp)) {
		rdp->n_rp_cpu_needs_gp++;
		return 1;
	}

	/* Has another RCU grace period completed?  */
	if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
		rdp->n_rp_gp_completed++;
		return 1;
	}

	/* Has a new RCU grace period started? */
	if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
	    unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */
		rdp->n_rp_gp_started++;
		return 1;
	}

	/* Does this CPU need a deferred NOCB wakeup? */
	if (rcu_nocb_need_deferred_wakeup(rdp)) {
		rdp->n_rp_nocb_defer_wakeup++;
		return 1;
	}

	/* nothing to do */
	rdp->n_rp_need_nothing++;
	return 0;
}

/*
 * Check to see if there is any immediate RCU-related work to be done
 * by the current CPU, returning 1 if so.  This function is part of the
 * RCU implementation; it is -not- an exported member of the RCU API.
 */
static int rcu_pending(void)
{
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
		if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
			return 1;
	return 0;
}

/*
 * Return true if the specified CPU has any callback.  If all_lazy is
 * non-NULL, store an indication of whether all callbacks are lazy.
 * (If there are no callbacks, all of them are deemed to be lazy.)
 */
static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
{
	bool al = true;
	bool hc = false;
	struct rcu_data *rdp;
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		if (!rdp->nxtlist)
			continue;
		hc = true;
		if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
			al = false;
			break;
		}
	}
	if (all_lazy)
		*all_lazy = al;
	return hc;
}

/*
 * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
 * the compiler is expected to optimize this away.
 */
static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
			       int cpu, unsigned long done)
{
	trace_rcu_barrier(rsp->name, s, cpu,
			  atomic_read(&rsp->barrier_cpu_count), done);
}

/*
 * RCU callback function for _rcu_barrier().  If we are last, wake
 * up the task executing _rcu_barrier().
 */
static void rcu_barrier_callback(struct rcu_head *rhp)
{
	struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
	struct rcu_state *rsp = rdp->rsp;

	if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
		_rcu_barrier_trace(rsp, "LastCB", -1, rsp->barrier_sequence);
		complete(&rsp->barrier_completion);
	} else {
		_rcu_barrier_trace(rsp, "CB", -1, rsp->barrier_sequence);
	}
}

/*
 * Called with preemption disabled, and from cross-cpu IRQ context.
 */
static void rcu_barrier_func(void *type)
{
	struct rcu_state *rsp = type;
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);

	_rcu_barrier_trace(rsp, "IRQ", -1, rsp->barrier_sequence);
	atomic_inc(&rsp->barrier_cpu_count);
	rsp->call(&rdp->barrier_head, rcu_barrier_callback);
}

/*
 * Orchestrate the specified type of RCU barrier, waiting for all
 * RCU callbacks of the specified type to complete.
 */
static void _rcu_barrier(struct rcu_state *rsp)
{
	int cpu;
	struct rcu_data *rdp;
	unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);

	_rcu_barrier_trace(rsp, "Begin", -1, s);

	/* Take mutex to serialize concurrent rcu_barrier() requests. */
	mutex_lock(&rsp->barrier_mutex);

	/* Did someone else do our work for us? */
	if (rcu_seq_done(&rsp->barrier_sequence, s)) {
		_rcu_barrier_trace(rsp, "EarlyExit", -1, rsp->barrier_sequence);
		smp_mb(); /* caller's subsequent code after above check. */
		mutex_unlock(&rsp->barrier_mutex);
		return;
	}

	/* Mark the start of the barrier operation. */
	rcu_seq_start(&rsp->barrier_sequence);
	_rcu_barrier_trace(rsp, "Inc1", -1, rsp->barrier_sequence);

	/*
	 * Initialize the count to one rather than to zero in order to
	 * avoid a too-soon return to zero in case of a short grace period
	 * (or preemption of this task).  Exclude CPU-hotplug operations
	 * to ensure that no offline CPU has callbacks queued.
	 */
	init_completion(&rsp->barrier_completion);
	atomic_set(&rsp->barrier_cpu_count, 1);
	get_online_cpus();

	/*
	 * Force each CPU with callbacks to register a new callback.
	 * When that callback is invoked, we will know that all of the
	 * corresponding CPU's preceding callbacks have been invoked.
	 */
	for_each_possible_cpu(cpu) {
		if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
			continue;
		rdp = per_cpu_ptr(rsp->rda, cpu);
		if (rcu_is_nocb_cpu(cpu)) {
			if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
				_rcu_barrier_trace(rsp, "OfflineNoCB", cpu,
						   rsp->barrier_sequence);
			} else {
				_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
						   rsp->barrier_sequence);
				smp_mb__before_atomic();
				atomic_inc(&rsp->barrier_cpu_count);
				__call_rcu(&rdp->barrier_head,
					   rcu_barrier_callback, rsp, cpu, 0);
			}
		} else if (READ_ONCE(rdp->qlen)) {
			_rcu_barrier_trace(rsp, "OnlineQ", cpu,
					   rsp->barrier_sequence);
			smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
		} else {
			_rcu_barrier_trace(rsp, "OnlineNQ", cpu,
					   rsp->barrier_sequence);
		}
	}
	put_online_cpus();

	/*
	 * Now that we have an rcu_barrier_callback() callback on each
	 * CPU, and thus each counted, remove the initial count.
	 */
	if (atomic_dec_and_test(&rsp->barrier_cpu_count))
		complete(&rsp->barrier_completion);

	/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
	wait_for_completion(&rsp->barrier_completion);

	/* Mark the end of the barrier operation. */
	_rcu_barrier_trace(rsp, "Inc2", -1, rsp->barrier_sequence);
	rcu_seq_end(&rsp->barrier_sequence);

	/* Other rcu_barrier() invocations can now safely proceed. */
	mutex_unlock(&rsp->barrier_mutex);
}

/**
 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 */
void rcu_barrier_bh(void)
{
	_rcu_barrier(&rcu_bh_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);

/**
 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 */
void rcu_barrier_sched(void)
{
	_rcu_barrier(&rcu_sched_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);

/*
 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
 * first CPU in a given leaf rcu_node structure coming online.  The caller
 * must hold the corresponding leaf rcu_node ->lock with interrrupts
 * disabled.
 */
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
{
	long mask;
	struct rcu_node *rnp = rnp_leaf;

	for (;;) {
		mask = rnp->grpmask;
		rnp = rnp->parent;
		if (rnp == NULL)
			return;
		raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
		rnp->qsmaskinit |= mask;
		raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
	}
}

/*
 * Do boot-time initialization of a CPU's per-CPU RCU data.
 */
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
{
	unsigned long flags;
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
	struct rcu_node *rnp = rcu_get_root(rsp);

	/* Set up local state, ensuring consistent view of global state. */
	raw_spin_lock_irqsave_rcu_node(rnp, flags);
	rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
	WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
	rdp->cpu = cpu;
	rdp->rsp = rsp;
	rcu_boot_init_nocb_percpu_data(rdp);
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}

/*
 * Initialize a CPU's per-CPU RCU data.  Note that only one online or
 * offline event can be happening at a given time.  Note also that we
 * can accept some slop in the rsp->completed access due to the fact
 * that this CPU cannot possibly have any RCU callbacks in flight yet.
 */
static void
rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
{
	unsigned long flags;
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
	struct rcu_node *rnp = rcu_get_root(rsp);

	/* Set up local state, ensuring consistent view of global state. */
	raw_spin_lock_irqsave_rcu_node(rnp, flags);
	rdp->qlen_last_fqs_check = 0;
	rdp->n_force_qs_snap = rsp->n_force_qs;
	rdp->blimit = blimit;
	if (!rdp->nxtlist)
		init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
	rcu_sysidle_init_percpu_data(rdp->dynticks);
	rcu_dynticks_eqs_online();
	raw_spin_unlock_rcu_node(rnp);		/* irqs remain disabled. */

	/*
	 * Add CPU to leaf rcu_node pending-online bitmask.  Any needed
	 * propagation up the rcu_node tree will happen at the beginning
	 * of the next grace period.
	 */
	rnp = rdp->mynode;
	raw_spin_lock_rcu_node(rnp);		/* irqs already disabled. */
	if (!rdp->beenonline)
		WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1);
	rdp->beenonline = true;	 /* We have now been online. */
	rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
	rdp->completed = rnp->completed;
	rdp->cpu_no_qs.b.norm = true;
	rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu);
	rdp->core_needs_qs = false;
	trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}

int rcutree_prepare_cpu(unsigned int cpu)
{
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
		rcu_init_percpu_data(cpu, rsp);

	rcu_prepare_kthreads(cpu);
	rcu_spawn_all_nocb_kthreads(cpu);

	return 0;
}

static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
{
	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);

	rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
}

int rcutree_online_cpu(unsigned int cpu)
{
	sync_sched_exp_online_cleanup(cpu);
	rcutree_affinity_setting(cpu, -1);
	return 0;
}

int rcutree_offline_cpu(unsigned int cpu)
{
	rcutree_affinity_setting(cpu, cpu);
	return 0;
}


int rcutree_dying_cpu(unsigned int cpu)
{
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
		rcu_cleanup_dying_cpu(rsp);
	return 0;
}

int rcutree_dead_cpu(unsigned int cpu)
{
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp) {
		rcu_cleanup_dead_cpu(cpu, rsp);
		do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
	}
	return 0;
}

/*
 * Mark the specified CPU as being online so that subsequent grace periods
 * (both expedited and normal) will wait on it.  Note that this means that
 * incoming CPUs are not allowed to use RCU read-side critical sections
 * until this function is called.  Failing to observe this restriction
 * will result in lockdep splats.
 */
void rcu_cpu_starting(unsigned int cpu)
{
	unsigned long flags;
	unsigned long mask;
	struct rcu_data *rdp;
	struct rcu_node *rnp;
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp) {
		rdp = per_cpu_ptr(rsp->rda, cpu);
		rnp = rdp->mynode;
		mask = rdp->grpmask;
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		rnp->qsmaskinitnext |= mask;
		rnp->expmaskinitnext |= mask;
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
	}
}

#ifdef CONFIG_HOTPLUG_CPU
/*
 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
 * function.  We now remove it from the rcu_node tree's ->qsmaskinit
 * bit masks.
 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
 * function.  We now remove it from the rcu_node tree's ->qsmaskinit
 * bit masks.
 */
static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
{
	unsigned long flags;
	unsigned long mask;
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */

	/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
	mask = rdp->grpmask;
	raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
	rnp->qsmaskinitnext &= ~mask;
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}

void rcu_report_dead(unsigned int cpu)
{
	struct rcu_state *rsp;

	/* QS for any half-done expedited RCU-sched GP. */
	preempt_disable();
	rcu_report_exp_rdp(&rcu_sched_state,
			   this_cpu_ptr(rcu_sched_state.rda), true);
	preempt_enable();
	for_each_rcu_flavor(rsp)
		rcu_cleanup_dying_idle_cpu(cpu, rsp);
}
#endif

static int rcu_pm_notify(struct notifier_block *self,
			 unsigned long action, void *hcpu)
{
	switch (action) {
	case PM_HIBERNATION_PREPARE:
	case PM_SUSPEND_PREPARE:
		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
			rcu_expedite_gp();
		break;
	case PM_POST_HIBERNATION:
	case PM_POST_SUSPEND:
		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
			rcu_unexpedite_gp();
		break;
	default:
		break;
	}
	return NOTIFY_OK;
}

/*
 * Spawn the kthreads that handle each RCU flavor's grace periods.
 */
static int __init rcu_spawn_gp_kthread(void)
{
	unsigned long flags;
	int kthread_prio_in = kthread_prio;
	struct rcu_node *rnp;
	struct rcu_state *rsp;
	struct sched_param sp;
	struct task_struct *t;

	/* Force priority into range. */
	if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
		kthread_prio = 1;
	else if (kthread_prio < 0)
		kthread_prio = 0;
	else if (kthread_prio > 99)
		kthread_prio = 99;
	if (kthread_prio != kthread_prio_in)
		pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
			 kthread_prio, kthread_prio_in);

	rcu_scheduler_fully_active = 1;
	for_each_rcu_flavor(rsp) {
		t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
		BUG_ON(IS_ERR(t));
		rnp = rcu_get_root(rsp);
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		rsp->gp_kthread = t;
		if (kthread_prio) {
			sp.sched_priority = kthread_prio;
			sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
		}
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		wake_up_process(t);
	}
	rcu_spawn_nocb_kthreads();
	rcu_spawn_boost_kthreads();
	return 0;
}
early_initcall(rcu_spawn_gp_kthread);

/*
 * This function is invoked towards the end of the scheduler's
 * initialization process.  Before this is called, the idle task might
 * contain synchronous grace-period primitives (during which time, this idle
 * task is booting the system, and such primitives are no-ops).  After this
 * function is called, any synchronous grace-period primitives are run as
 * expedited, with the requesting task driving the grace period forward.
 * A later core_initcall() rcu_exp_runtime_mode() will switch to full
 * runtime RCU functionality.
 */
void rcu_scheduler_starting(void)
{
	WARN_ON(num_online_cpus() != 1);
	WARN_ON(nr_context_switches() > 0);
	rcu_test_sync_prims();
	rcu_scheduler_active = RCU_SCHEDULER_INIT;
	rcu_test_sync_prims();
}

/*
 * Compute the per-level fanout, either using the exact fanout specified
 * or balancing the tree, depending on the rcu_fanout_exact boot parameter.
 */
static void __init rcu_init_levelspread(int *levelspread, const int *levelcnt)
{
	int i;

	if (rcu_fanout_exact) {
		levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
		for (i = rcu_num_lvls - 2; i >= 0; i--)
			levelspread[i] = RCU_FANOUT;
	} else {
		int ccur;
		int cprv;

		cprv = nr_cpu_ids;
		for (i = rcu_num_lvls - 1; i >= 0; i--) {
			ccur = levelcnt[i];
			levelspread[i] = (cprv + ccur - 1) / ccur;
			cprv = ccur;
		}
	}
}

/*
 * Helper function for rcu_init() that initializes one rcu_state structure.
 */
static void __init rcu_init_one(struct rcu_state *rsp)
{
	static const char * const buf[] = RCU_NODE_NAME_INIT;
	static const char * const fqs[] = RCU_FQS_NAME_INIT;
	static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
	static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
	static u8 fl_mask = 0x1;

	int levelcnt[RCU_NUM_LVLS];		/* # nodes in each level. */
	int levelspread[RCU_NUM_LVLS];		/* kids/node in each level. */
	int cpustride = 1;
	int i;
	int j;
	struct rcu_node *rnp;

	BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */

	/* Silence gcc 4.8 false positive about array index out of range. */
	if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
		panic("rcu_init_one: rcu_num_lvls out of range");

	/* Initialize the level-tracking arrays. */

	for (i = 0; i < rcu_num_lvls; i++)
		levelcnt[i] = num_rcu_lvl[i];
	for (i = 1; i < rcu_num_lvls; i++)
		rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];
	rcu_init_levelspread(levelspread, levelcnt);
	rsp->flavor_mask = fl_mask;
	fl_mask <<= 1;

	/* Initialize the elements themselves, starting from the leaves. */

	for (i = rcu_num_lvls - 1; i >= 0; i--) {
		cpustride *= levelspread[i];
		rnp = rsp->level[i];
		for (j = 0; j < levelcnt[i]; j++, rnp++) {
			raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
			lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
						   &rcu_node_class[i], buf[i]);
			raw_spin_lock_init(&rnp->fqslock);
			lockdep_set_class_and_name(&rnp->fqslock,
						   &rcu_fqs_class[i], fqs[i]);
			rnp->gpnum = rsp->gpnum;
			rnp->completed = rsp->completed;
			rnp->qsmask = 0;
			rnp->qsmaskinit = 0;
			rnp->grplo = j * cpustride;
			rnp->grphi = (j + 1) * cpustride - 1;
			if (rnp->grphi >= nr_cpu_ids)
				rnp->grphi = nr_cpu_ids - 1;
			if (i == 0) {
				rnp->grpnum = 0;
				rnp->grpmask = 0;
				rnp->parent = NULL;
			} else {
				rnp->grpnum = j % levelspread[i - 1];
				rnp->grpmask = 1UL << rnp->grpnum;
				rnp->parent = rsp->level[i - 1] +
					      j / levelspread[i - 1];
			}
			rnp->level = i;
			INIT_LIST_HEAD(&rnp->blkd_tasks);
			rcu_init_one_nocb(rnp);
			init_waitqueue_head(&rnp->exp_wq[0]);
			init_waitqueue_head(&rnp->exp_wq[1]);
			init_waitqueue_head(&rnp->exp_wq[2]);
			init_waitqueue_head(&rnp->exp_wq[3]);
			spin_lock_init(&rnp->exp_lock);
		}
	}

	init_swait_queue_head(&rsp->gp_wq);
	init_swait_queue_head(&rsp->expedited_wq);
	rnp = rsp->level[rcu_num_lvls - 1];
	for_each_possible_cpu(i) {
		while (i > rnp->grphi)
			rnp++;
		per_cpu_ptr(rsp->rda, i)->mynode = rnp;
		rcu_boot_init_percpu_data(i, rsp);
	}
	list_add(&rsp->flavors, &rcu_struct_flavors);
}

/*
 * Compute the rcu_node tree geometry from kernel parameters.  This cannot
 * replace the definitions in tree.h because those are needed to size
 * the ->node array in the rcu_state structure.
 */
static void __init rcu_init_geometry(void)
{
	ulong d;
	int i;
	int rcu_capacity[RCU_NUM_LVLS];

	/*
	 * Initialize any unspecified boot parameters.
	 * The default values of jiffies_till_first_fqs and
	 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
	 * value, which is a function of HZ, then adding one for each
	 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
	 */
	d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
	if (jiffies_till_first_fqs == ULONG_MAX)
		jiffies_till_first_fqs = d;
	if (jiffies_till_next_fqs == ULONG_MAX)
		jiffies_till_next_fqs = d;

	/* If the compile-time values are accurate, just leave. */
	if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
	    nr_cpu_ids == NR_CPUS)
		return;
	pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
		rcu_fanout_leaf, nr_cpu_ids);

	/*
	 * The boot-time rcu_fanout_leaf parameter must be at least two
	 * and cannot exceed the number of bits in the rcu_node masks.
	 * Complain and fall back to the compile-time values if this
	 * limit is exceeded.
	 */
	if (rcu_fanout_leaf < 2 ||
	    rcu_fanout_leaf > sizeof(unsigned long) * 8) {
		rcu_fanout_leaf = RCU_FANOUT_LEAF;
		WARN_ON(1);
		return;
	}

	/*
	 * Compute number of nodes that can be handled an rcu_node tree
	 * with the given number of levels.
	 */
	rcu_capacity[0] = rcu_fanout_leaf;
	for (i = 1; i < RCU_NUM_LVLS; i++)
		rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;

	/*
	 * The tree must be able to accommodate the configured number of CPUs.
	 * If this limit is exceeded, fall back to the compile-time values.
	 */
	if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
		rcu_fanout_leaf = RCU_FANOUT_LEAF;
		WARN_ON(1);
		return;
	}

	/* Calculate the number of levels in the tree. */
	for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
	}
	rcu_num_lvls = i + 1;

	/* Calculate the number of rcu_nodes at each level of the tree. */
	for (i = 0; i < rcu_num_lvls; i++) {
		int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
		num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
	}

	/* Calculate the total number of rcu_node structures. */
	rcu_num_nodes = 0;
	for (i = 0; i < rcu_num_lvls; i++)
		rcu_num_nodes += num_rcu_lvl[i];
}

/*
 * Dump out the structure of the rcu_node combining tree associated
 * with the rcu_state structure referenced by rsp.
 */
static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
{
	int level = 0;
	struct rcu_node *rnp;

	pr_info("rcu_node tree layout dump\n");
	pr_info(" ");
	rcu_for_each_node_breadth_first(rsp, rnp) {
		if (rnp->level != level) {
			pr_cont("\n");
			pr_info(" ");
			level = rnp->level;
		}
		pr_cont("%d:%d ^%d  ", rnp->grplo, rnp->grphi, rnp->grpnum);
	}
	pr_cont("\n");
}

void __init rcu_init(void)
{
	int cpu;

	rcu_early_boot_tests();

	rcu_bootup_announce();
	rcu_init_geometry();
	rcu_init_one(&rcu_bh_state);
	rcu_init_one(&rcu_sched_state);
	if (dump_tree)
		rcu_dump_rcu_node_tree(&rcu_sched_state);
	__rcu_init_preempt();
	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);

	/*
	 * We don't need protection against CPU-hotplug here because
	 * this is called early in boot, before either interrupts
	 * or the scheduler are operational.
	 */
	pm_notifier(rcu_pm_notify, 0);
	for_each_online_cpu(cpu) {
		rcutree_prepare_cpu(cpu);
		rcu_cpu_starting(cpu);
	}
}

#include "tree_exp.h"
#include "tree_plugin.h"