summaryrefslogtreecommitdiff
path: root/fs/jbd2/transaction.c
blob: 43985738aa860d91d1ecda400783cc99eae6ed2b (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
// SPDX-License-Identifier: GPL-2.0+
/*
 * linux/fs/jbd2/transaction.c
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
 *
 * Copyright 1998 Red Hat corp --- All Rights Reserved
 *
 * Generic filesystem transaction handling code; part of the ext2fs
 * journaling system.
 *
 * This file manages transactions (compound commits managed by the
 * journaling code) and handles (individual atomic operations by the
 * filesystem).
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd2.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/hrtimer.h>
#include <linux/backing-dev.h>
#include <linux/bug.h>
#include <linux/module.h>
#include <linux/sched/mm.h>

#include <trace/events/jbd2.h>

static void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh);
static void __jbd2_journal_unfile_buffer(struct journal_head *jh);

static struct kmem_cache *transaction_cache;
int __init jbd2_journal_init_transaction_cache(void)
{
	J_ASSERT(!transaction_cache);
	transaction_cache = kmem_cache_create("jbd2_transaction_s",
					sizeof(transaction_t),
					0,
					SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY,
					NULL);
	if (!transaction_cache) {
		pr_emerg("JBD2: failed to create transaction cache\n");
		return -ENOMEM;
	}
	return 0;
}

void jbd2_journal_destroy_transaction_cache(void)
{
	kmem_cache_destroy(transaction_cache);
	transaction_cache = NULL;
}

void jbd2_journal_free_transaction(transaction_t *transaction)
{
	if (unlikely(ZERO_OR_NULL_PTR(transaction)))
		return;
	kmem_cache_free(transaction_cache, transaction);
}

/*
 * Base amount of descriptor blocks we reserve for each transaction.
 */
static int jbd2_descriptor_blocks_per_trans(journal_t *journal)
{
	int tag_space = journal->j_blocksize - sizeof(journal_header_t);
	int tags_per_block;

	/* Subtract UUID */
	tag_space -= 16;
	if (jbd2_journal_has_csum_v2or3(journal))
		tag_space -= sizeof(struct jbd2_journal_block_tail);
	/* Commit code leaves a slack space of 16 bytes at the end of block */
	tags_per_block = (tag_space - 16) / journal_tag_bytes(journal);
	/*
	 * Revoke descriptors are accounted separately so we need to reserve
	 * space for commit block and normal transaction descriptor blocks.
	 */
	return 1 + DIV_ROUND_UP(journal->j_max_transaction_buffers,
				tags_per_block);
}

/*
 * jbd2_get_transaction: obtain a new transaction_t object.
 *
 * Simply initialise a new transaction. Initialize it in
 * RUNNING state and add it to the current journal (which should not
 * have an existing running transaction: we only make a new transaction
 * once we have started to commit the old one).
 *
 * Preconditions:
 *	The journal MUST be locked.  We don't perform atomic mallocs on the
 *	new transaction	and we can't block without protecting against other
 *	processes trying to touch the journal while it is in transition.
 *
 */

static void jbd2_get_transaction(journal_t *journal,
				transaction_t *transaction)
{
	transaction->t_journal = journal;
	transaction->t_state = T_RUNNING;
	transaction->t_start_time = ktime_get();
	transaction->t_tid = journal->j_transaction_sequence++;
	transaction->t_expires = jiffies + journal->j_commit_interval;
	spin_lock_init(&transaction->t_handle_lock);
	atomic_set(&transaction->t_updates, 0);
	atomic_set(&transaction->t_outstanding_credits,
		   jbd2_descriptor_blocks_per_trans(journal) +
		   atomic_read(&journal->j_reserved_credits));
	atomic_set(&transaction->t_outstanding_revokes, 0);
	atomic_set(&transaction->t_handle_count, 0);
	INIT_LIST_HEAD(&transaction->t_inode_list);
	INIT_LIST_HEAD(&transaction->t_private_list);

	/* Set up the commit timer for the new transaction. */
	journal->j_commit_timer.expires = round_jiffies_up(transaction->t_expires);
	add_timer(&journal->j_commit_timer);

	J_ASSERT(journal->j_running_transaction == NULL);
	journal->j_running_transaction = transaction;
	transaction->t_max_wait = 0;
	transaction->t_start = jiffies;
	transaction->t_requested = 0;
}

/*
 * Handle management.
 *
 * A handle_t is an object which represents a single atomic update to a
 * filesystem, and which tracks all of the modifications which form part
 * of that one update.
 */

/*
 * Update transaction's maximum wait time, if debugging is enabled.
 *
 * In order for t_max_wait to be reliable, it must be protected by a
 * lock.  But doing so will mean that start_this_handle() can not be
 * run in parallel on SMP systems, which limits our scalability.  So
 * unless debugging is enabled, we no longer update t_max_wait, which
 * means that maximum wait time reported by the jbd2_run_stats
 * tracepoint will always be zero.
 */
static inline void update_t_max_wait(transaction_t *transaction,
				     unsigned long ts)
{
#ifdef CONFIG_JBD2_DEBUG
	if (jbd2_journal_enable_debug &&
	    time_after(transaction->t_start, ts)) {
		ts = jbd2_time_diff(ts, transaction->t_start);
		spin_lock(&transaction->t_handle_lock);
		if (ts > transaction->t_max_wait)
			transaction->t_max_wait = ts;
		spin_unlock(&transaction->t_handle_lock);
	}
#endif
}

/*
 * Wait until running transaction passes to T_FLUSH state and new transaction
 * can thus be started. Also starts the commit if needed. The function expects
 * running transaction to exist and releases j_state_lock.
 */
static void wait_transaction_locked(journal_t *journal)
	__releases(journal->j_state_lock)
{
	DEFINE_WAIT(wait);
	int need_to_start;
	tid_t tid = journal->j_running_transaction->t_tid;

	prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
			TASK_UNINTERRUPTIBLE);
	need_to_start = !tid_geq(journal->j_commit_request, tid);
	read_unlock(&journal->j_state_lock);
	if (need_to_start)
		jbd2_log_start_commit(journal, tid);
	jbd2_might_wait_for_commit(journal);
	schedule();
	finish_wait(&journal->j_wait_transaction_locked, &wait);
}

/*
 * Wait until running transaction transitions from T_SWITCH to T_FLUSH
 * state and new transaction can thus be started. The function releases
 * j_state_lock.
 */
static void wait_transaction_switching(journal_t *journal)
	__releases(journal->j_state_lock)
{
	DEFINE_WAIT(wait);

	if (WARN_ON(!journal->j_running_transaction ||
		    journal->j_running_transaction->t_state != T_SWITCH))
		return;
	prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
			TASK_UNINTERRUPTIBLE);
	read_unlock(&journal->j_state_lock);
	/*
	 * We don't call jbd2_might_wait_for_commit() here as there's no
	 * waiting for outstanding handles happening anymore in T_SWITCH state
	 * and handling of reserved handles actually relies on that for
	 * correctness.
	 */
	schedule();
	finish_wait(&journal->j_wait_transaction_locked, &wait);
}

static void sub_reserved_credits(journal_t *journal, int blocks)
{
	atomic_sub(blocks, &journal->j_reserved_credits);
	wake_up(&journal->j_wait_reserved);
}

/*
 * Wait until we can add credits for handle to the running transaction.  Called
 * with j_state_lock held for reading. Returns 0 if handle joined the running
 * transaction. Returns 1 if we had to wait, j_state_lock is dropped, and
 * caller must retry.
 */
static int add_transaction_credits(journal_t *journal, int blocks,
				   int rsv_blocks)
{
	transaction_t *t = journal->j_running_transaction;
	int needed;
	int total = blocks + rsv_blocks;

	/*
	 * If the current transaction is locked down for commit, wait
	 * for the lock to be released.
	 */
	if (t->t_state != T_RUNNING) {
		WARN_ON_ONCE(t->t_state >= T_FLUSH);
		wait_transaction_locked(journal);
		return 1;
	}

	/*
	 * If there is not enough space left in the log to write all
	 * potential buffers requested by this operation, we need to
	 * stall pending a log checkpoint to free some more log space.
	 */
	needed = atomic_add_return(total, &t->t_outstanding_credits);
	if (needed > journal->j_max_transaction_buffers) {
		/*
		 * If the current transaction is already too large,
		 * then start to commit it: we can then go back and
		 * attach this handle to a new transaction.
		 */
		atomic_sub(total, &t->t_outstanding_credits);

		/*
		 * Is the number of reserved credits in the current transaction too
		 * big to fit this handle? Wait until reserved credits are freed.
		 */
		if (atomic_read(&journal->j_reserved_credits) + total >
		    journal->j_max_transaction_buffers) {
			read_unlock(&journal->j_state_lock);
			jbd2_might_wait_for_commit(journal);
			wait_event(journal->j_wait_reserved,
				   atomic_read(&journal->j_reserved_credits) + total <=
				   journal->j_max_transaction_buffers);
			return 1;
		}

		wait_transaction_locked(journal);
		return 1;
	}

	/*
	 * The commit code assumes that it can get enough log space
	 * without forcing a checkpoint.  This is *critical* for
	 * correctness: a checkpoint of a buffer which is also
	 * associated with a committing transaction creates a deadlock,
	 * so commit simply cannot force through checkpoints.
	 *
	 * We must therefore ensure the necessary space in the journal
	 * *before* starting to dirty potentially checkpointed buffers
	 * in the new transaction.
	 */
	if (jbd2_log_space_left(journal) < journal->j_max_transaction_buffers) {
		atomic_sub(total, &t->t_outstanding_credits);
		read_unlock(&journal->j_state_lock);
		jbd2_might_wait_for_commit(journal);
		write_lock(&journal->j_state_lock);
		if (jbd2_log_space_left(journal) <
					journal->j_max_transaction_buffers)
			__jbd2_log_wait_for_space(journal);
		write_unlock(&journal->j_state_lock);
		return 1;
	}

	/* No reservation? We are done... */
	if (!rsv_blocks)
		return 0;

	needed = atomic_add_return(rsv_blocks, &journal->j_reserved_credits);
	/* We allow at most half of a transaction to be reserved */
	if (needed > journal->j_max_transaction_buffers / 2) {
		sub_reserved_credits(journal, rsv_blocks);
		atomic_sub(total, &t->t_outstanding_credits);
		read_unlock(&journal->j_state_lock);
		jbd2_might_wait_for_commit(journal);
		wait_event(journal->j_wait_reserved,
			 atomic_read(&journal->j_reserved_credits) + rsv_blocks
			 <= journal->j_max_transaction_buffers / 2);
		return 1;
	}
	return 0;
}

/*
 * start_this_handle: Given a handle, deal with any locking or stalling
 * needed to make sure that there is enough journal space for the handle
 * to begin.  Attach the handle to a transaction and set up the
 * transaction's buffer credits.
 */

static int start_this_handle(journal_t *journal, handle_t *handle,
			     gfp_t gfp_mask)
{
	transaction_t	*transaction, *new_transaction = NULL;
	int		blocks = handle->h_total_credits;
	int		rsv_blocks = 0;
	unsigned long ts = jiffies;

	if (handle->h_rsv_handle)
		rsv_blocks = handle->h_rsv_handle->h_total_credits;

	/*
	 * Limit the number of reserved credits to 1/2 of maximum transaction
	 * size and limit the number of total credits to not exceed maximum
	 * transaction size per operation.
	 */
	if ((rsv_blocks > journal->j_max_transaction_buffers / 2) ||
	    (rsv_blocks + blocks > journal->j_max_transaction_buffers)) {
		printk(KERN_ERR "JBD2: %s wants too many credits "
		       "credits:%d rsv_credits:%d max:%d\n",
		       current->comm, blocks, rsv_blocks,
		       journal->j_max_transaction_buffers);
		WARN_ON(1);
		return -ENOSPC;
	}

alloc_transaction:
	if (!journal->j_running_transaction) {
		/*
		 * If __GFP_FS is not present, then we may be being called from
		 * inside the fs writeback layer, so we MUST NOT fail.
		 */
		if ((gfp_mask & __GFP_FS) == 0)
			gfp_mask |= __GFP_NOFAIL;
		new_transaction = kmem_cache_zalloc(transaction_cache,
						    gfp_mask);
		if (!new_transaction)
			return -ENOMEM;
	}

	jbd_debug(3, "New handle %p going live.\n", handle);

	/*
	 * We need to hold j_state_lock until t_updates has been incremented,
	 * for proper journal barrier handling
	 */
repeat:
	read_lock(&journal->j_state_lock);
	BUG_ON(journal->j_flags & JBD2_UNMOUNT);
	if (is_journal_aborted(journal) ||
	    (journal->j_errno != 0 && !(journal->j_flags & JBD2_ACK_ERR))) {
		read_unlock(&journal->j_state_lock);
		jbd2_journal_free_transaction(new_transaction);
		return -EROFS;
	}

	/*
	 * Wait on the journal's transaction barrier if necessary. Specifically
	 * we allow reserved handles to proceed because otherwise commit could
	 * deadlock on page writeback not being able to complete.
	 */
	if (!handle->h_reserved && journal->j_barrier_count) {
		read_unlock(&journal->j_state_lock);
		wait_event(journal->j_wait_transaction_locked,
				journal->j_barrier_count == 0);
		goto repeat;
	}

	if (!journal->j_running_transaction) {
		read_unlock(&journal->j_state_lock);
		if (!new_transaction)
			goto alloc_transaction;
		write_lock(&journal->j_state_lock);
		if (!journal->j_running_transaction &&
		    (handle->h_reserved || !journal->j_barrier_count)) {
			jbd2_get_transaction(journal, new_transaction);
			new_transaction = NULL;
		}
		write_unlock(&journal->j_state_lock);
		goto repeat;
	}

	transaction = journal->j_running_transaction;

	if (!handle->h_reserved) {
		/* We may have dropped j_state_lock - restart in that case */
		if (add_transaction_credits(journal, blocks, rsv_blocks))
			goto repeat;
	} else {
		/*
		 * We have handle reserved so we are allowed to join T_LOCKED
		 * transaction and we don't have to check for transaction size
		 * and journal space. But we still have to wait while running
		 * transaction is being switched to a committing one as it
		 * won't wait for any handles anymore.
		 */
		if (transaction->t_state == T_SWITCH) {
			wait_transaction_switching(journal);
			goto repeat;
		}
		sub_reserved_credits(journal, blocks);
		handle->h_reserved = 0;
	}

	/* OK, account for the buffers that this operation expects to
	 * use and add the handle to the running transaction. 
	 */
	update_t_max_wait(transaction, ts);
	handle->h_transaction = transaction;
	handle->h_requested_credits = blocks;
	handle->h_revoke_credits_requested = handle->h_revoke_credits;
	handle->h_start_jiffies = jiffies;
	atomic_inc(&transaction->t_updates);
	atomic_inc(&transaction->t_handle_count);
	jbd_debug(4, "Handle %p given %d credits (total %d, free %lu)\n",
		  handle, blocks,
		  atomic_read(&transaction->t_outstanding_credits),
		  jbd2_log_space_left(journal));
	read_unlock(&journal->j_state_lock);
	current->journal_info = handle;

	rwsem_acquire_read(&journal->j_trans_commit_map, 0, 0, _THIS_IP_);
	jbd2_journal_free_transaction(new_transaction);
	/*
	 * Ensure that no allocations done while the transaction is open are
	 * going to recurse back to the fs layer.
	 */
	handle->saved_alloc_context = memalloc_nofs_save();
	return 0;
}

/* Allocate a new handle.  This should probably be in a slab... */
static handle_t *new_handle(int nblocks)
{
	handle_t *handle = jbd2_alloc_handle(GFP_NOFS);
	if (!handle)
		return NULL;
	handle->h_total_credits = nblocks;
	handle->h_ref = 1;

	return handle;
}

handle_t *jbd2__journal_start(journal_t *journal, int nblocks, int rsv_blocks,
			      int revoke_records, gfp_t gfp_mask,
			      unsigned int type, unsigned int line_no)
{
	handle_t *handle = journal_current_handle();
	int err;

	if (!journal)
		return ERR_PTR(-EROFS);

	if (handle) {
		J_ASSERT(handle->h_transaction->t_journal == journal);
		handle->h_ref++;
		return handle;
	}

	nblocks += DIV_ROUND_UP(revoke_records,
				journal->j_revoke_records_per_block);
	handle = new_handle(nblocks);
	if (!handle)
		return ERR_PTR(-ENOMEM);
	if (rsv_blocks) {
		handle_t *rsv_handle;

		rsv_handle = new_handle(rsv_blocks);
		if (!rsv_handle) {
			jbd2_free_handle(handle);
			return ERR_PTR(-ENOMEM);
		}
		rsv_handle->h_reserved = 1;
		rsv_handle->h_journal = journal;
		handle->h_rsv_handle = rsv_handle;
	}
	handle->h_revoke_credits = revoke_records;

	err = start_this_handle(journal, handle, gfp_mask);
	if (err < 0) {
		if (handle->h_rsv_handle)
			jbd2_free_handle(handle->h_rsv_handle);
		jbd2_free_handle(handle);
		return ERR_PTR(err);
	}
	handle->h_type = type;
	handle->h_line_no = line_no;
	trace_jbd2_handle_start(journal->j_fs_dev->bd_dev,
				handle->h_transaction->t_tid, type,
				line_no, nblocks);

	return handle;
}
EXPORT_SYMBOL(jbd2__journal_start);


/**
 * handle_t *jbd2_journal_start() - Obtain a new handle.
 * @journal: Journal to start transaction on.
 * @nblocks: number of block buffer we might modify
 *
 * We make sure that the transaction can guarantee at least nblocks of
 * modified buffers in the log.  We block until the log can guarantee
 * that much space. Additionally, if rsv_blocks > 0, we also create another
 * handle with rsv_blocks reserved blocks in the journal. This handle is
 * stored in h_rsv_handle. It is not attached to any particular transaction
 * and thus doesn't block transaction commit. If the caller uses this reserved
 * handle, it has to set h_rsv_handle to NULL as otherwise jbd2_journal_stop()
 * on the parent handle will dispose the reserved one. Reserved handle has to
 * be converted to a normal handle using jbd2_journal_start_reserved() before
 * it can be used.
 *
 * Return a pointer to a newly allocated handle, or an ERR_PTR() value
 * on failure.
 */
handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
{
	return jbd2__journal_start(journal, nblocks, 0, 0, GFP_NOFS, 0, 0);
}
EXPORT_SYMBOL(jbd2_journal_start);

static void __jbd2_journal_unreserve_handle(handle_t *handle, transaction_t *t)
{
	journal_t *journal = handle->h_journal;

	WARN_ON(!handle->h_reserved);
	sub_reserved_credits(journal, handle->h_total_credits);
	if (t)
		atomic_sub(handle->h_total_credits, &t->t_outstanding_credits);
}

void jbd2_journal_free_reserved(handle_t *handle)
{
	journal_t *journal = handle->h_journal;

	/* Get j_state_lock to pin running transaction if it exists */
	read_lock(&journal->j_state_lock);
	__jbd2_journal_unreserve_handle(handle, journal->j_running_transaction);
	read_unlock(&journal->j_state_lock);
	jbd2_free_handle(handle);
}
EXPORT_SYMBOL(jbd2_journal_free_reserved);

/**
 * int jbd2_journal_start_reserved() - start reserved handle
 * @handle: handle to start
 * @type: for handle statistics
 * @line_no: for handle statistics
 *
 * Start handle that has been previously reserved with jbd2_journal_reserve().
 * This attaches @handle to the running transaction (or creates one if there's
 * not transaction running). Unlike jbd2_journal_start() this function cannot
 * block on journal commit, checkpointing, or similar stuff. It can block on
 * memory allocation or frozen journal though.
 *
 * Return 0 on success, non-zero on error - handle is freed in that case.
 */
int jbd2_journal_start_reserved(handle_t *handle, unsigned int type,
				unsigned int line_no)
{
	journal_t *journal = handle->h_journal;
	int ret = -EIO;

	if (WARN_ON(!handle->h_reserved)) {
		/* Someone passed in normal handle? Just stop it. */
		jbd2_journal_stop(handle);
		return ret;
	}
	/*
	 * Usefulness of mixing of reserved and unreserved handles is
	 * questionable. So far nobody seems to need it so just error out.
	 */
	if (WARN_ON(current->journal_info)) {
		jbd2_journal_free_reserved(handle);
		return ret;
	}

	handle->h_journal = NULL;
	/*
	 * GFP_NOFS is here because callers are likely from writeback or
	 * similarly constrained call sites
	 */
	ret = start_this_handle(journal, handle, GFP_NOFS);
	if (ret < 0) {
		handle->h_journal = journal;
		jbd2_journal_free_reserved(handle);
		return ret;
	}
	handle->h_type = type;
	handle->h_line_no = line_no;
	trace_jbd2_handle_start(journal->j_fs_dev->bd_dev,
				handle->h_transaction->t_tid, type,
				line_no, handle->h_total_credits);
	return 0;
}
EXPORT_SYMBOL(jbd2_journal_start_reserved);

/**
 * int jbd2_journal_extend() - extend buffer credits.
 * @handle:  handle to 'extend'
 * @nblocks: nr blocks to try to extend by.
 * @revoke_records: number of revoke records to try to extend by.
 *
 * Some transactions, such as large extends and truncates, can be done
 * atomically all at once or in several stages.  The operation requests
 * a credit for a number of buffer modifications in advance, but can
 * extend its credit if it needs more.
 *
 * jbd2_journal_extend tries to give the running handle more buffer credits.
 * It does not guarantee that allocation - this is a best-effort only.
 * The calling process MUST be able to deal cleanly with a failure to
 * extend here.
 *
 * Return 0 on success, non-zero on failure.
 *
 * return code < 0 implies an error
 * return code > 0 implies normal transaction-full status.
 */
int jbd2_journal_extend(handle_t *handle, int nblocks, int revoke_records)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal;
	int result;
	int wanted;

	if (is_handle_aborted(handle))
		return -EROFS;
	journal = transaction->t_journal;

	result = 1;

	read_lock(&journal->j_state_lock);

	/* Don't extend a locked-down transaction! */
	if (transaction->t_state != T_RUNNING) {
		jbd_debug(3, "denied handle %p %d blocks: "
			  "transaction not running\n", handle, nblocks);
		goto error_out;
	}

	nblocks += DIV_ROUND_UP(
			handle->h_revoke_credits_requested + revoke_records,
			journal->j_revoke_records_per_block) -
		DIV_ROUND_UP(
			handle->h_revoke_credits_requested,
			journal->j_revoke_records_per_block);
	spin_lock(&transaction->t_handle_lock);
	wanted = atomic_add_return(nblocks,
				   &transaction->t_outstanding_credits);

	if (wanted > journal->j_max_transaction_buffers) {
		jbd_debug(3, "denied handle %p %d blocks: "
			  "transaction too large\n", handle, nblocks);
		atomic_sub(nblocks, &transaction->t_outstanding_credits);
		goto unlock;
	}

	trace_jbd2_handle_extend(journal->j_fs_dev->bd_dev,
				 transaction->t_tid,
				 handle->h_type, handle->h_line_no,
				 handle->h_total_credits,
				 nblocks);

	handle->h_total_credits += nblocks;
	handle->h_requested_credits += nblocks;
	handle->h_revoke_credits += revoke_records;
	handle->h_revoke_credits_requested += revoke_records;
	result = 0;

	jbd_debug(3, "extended handle %p by %d\n", handle, nblocks);
unlock:
	spin_unlock(&transaction->t_handle_lock);
error_out:
	read_unlock(&journal->j_state_lock);
	return result;
}

static void stop_this_handle(handle_t *handle)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal = transaction->t_journal;
	int revokes;

	J_ASSERT(journal_current_handle() == handle);
	J_ASSERT(atomic_read(&transaction->t_updates) > 0);
	current->journal_info = NULL;
	/*
	 * Subtract necessary revoke descriptor blocks from handle credits. We
	 * take care to account only for revoke descriptor blocks the
	 * transaction will really need as large sequences of transactions with
	 * small numbers of revokes are relatively common.
	 */
	revokes = handle->h_revoke_credits_requested - handle->h_revoke_credits;
	if (revokes) {
		int t_revokes, revoke_descriptors;
		int rr_per_blk = journal->j_revoke_records_per_block;

		WARN_ON_ONCE(DIV_ROUND_UP(revokes, rr_per_blk)
				> handle->h_total_credits);
		t_revokes = atomic_add_return(revokes,
				&transaction->t_outstanding_revokes);
		revoke_descriptors =
			DIV_ROUND_UP(t_revokes, rr_per_blk) -
			DIV_ROUND_UP(t_revokes - revokes, rr_per_blk);
		handle->h_total_credits -= revoke_descriptors;
	}
	atomic_sub(handle->h_total_credits,
		   &transaction->t_outstanding_credits);
	if (handle->h_rsv_handle)
		__jbd2_journal_unreserve_handle(handle->h_rsv_handle,
						transaction);
	if (atomic_dec_and_test(&transaction->t_updates))
		wake_up(&journal->j_wait_updates);

	rwsem_release(&journal->j_trans_commit_map, _THIS_IP_);
	/*
	 * Scope of the GFP_NOFS context is over here and so we can restore the
	 * original alloc context.
	 */
	memalloc_nofs_restore(handle->saved_alloc_context);
}

/**
 * int jbd2_journal_restart() - restart a handle .
 * @handle:  handle to restart
 * @nblocks: nr credits requested
 * @revoke_records: number of revoke record credits requested
 * @gfp_mask: memory allocation flags (for start_this_handle)
 *
 * Restart a handle for a multi-transaction filesystem
 * operation.
 *
 * If the jbd2_journal_extend() call above fails to grant new buffer credits
 * to a running handle, a call to jbd2_journal_restart will commit the
 * handle's transaction so far and reattach the handle to a new
 * transaction capable of guaranteeing the requested number of
 * credits. We preserve reserved handle if there's any attached to the
 * passed in handle.
 */
int jbd2__journal_restart(handle_t *handle, int nblocks, int revoke_records,
			  gfp_t gfp_mask)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal;
	tid_t		tid;
	int		need_to_start;
	int		ret;

	/* If we've had an abort of any type, don't even think about
	 * actually doing the restart! */
	if (is_handle_aborted(handle))
		return 0;
	journal = transaction->t_journal;
	tid = transaction->t_tid;

	/*
	 * First unlink the handle from its current transaction, and start the
	 * commit on that.
	 */
	jbd_debug(2, "restarting handle %p\n", handle);
	stop_this_handle(handle);
	handle->h_transaction = NULL;

	/*
	 * TODO: If we use READ_ONCE / WRITE_ONCE for j_commit_request we can
 	 * get rid of pointless j_state_lock traffic like this.
	 */
	read_lock(&journal->j_state_lock);
	need_to_start = !tid_geq(journal->j_commit_request, tid);
	read_unlock(&journal->j_state_lock);
	if (need_to_start)
		jbd2_log_start_commit(journal, tid);
	handle->h_total_credits = nblocks +
		DIV_ROUND_UP(revoke_records,
			     journal->j_revoke_records_per_block);
	handle->h_revoke_credits = revoke_records;
	ret = start_this_handle(journal, handle, gfp_mask);
	trace_jbd2_handle_restart(journal->j_fs_dev->bd_dev,
				 ret ? 0 : handle->h_transaction->t_tid,
				 handle->h_type, handle->h_line_no,
				 handle->h_total_credits);
	return ret;
}
EXPORT_SYMBOL(jbd2__journal_restart);


int jbd2_journal_restart(handle_t *handle, int nblocks)
{
	return jbd2__journal_restart(handle, nblocks, 0, GFP_NOFS);
}
EXPORT_SYMBOL(jbd2_journal_restart);

/**
 * void jbd2_journal_lock_updates () - establish a transaction barrier.
 * @journal:  Journal to establish a barrier on.
 *
 * This locks out any further updates from being started, and blocks
 * until all existing updates have completed, returning only once the
 * journal is in a quiescent state with no updates running.
 *
 * The journal lock should not be held on entry.
 */
void jbd2_journal_lock_updates(journal_t *journal)
{
	DEFINE_WAIT(wait);

	jbd2_might_wait_for_commit(journal);

	write_lock(&journal->j_state_lock);
	++journal->j_barrier_count;

	/* Wait until there are no reserved handles */
	if (atomic_read(&journal->j_reserved_credits)) {
		write_unlock(&journal->j_state_lock);
		wait_event(journal->j_wait_reserved,
			   atomic_read(&journal->j_reserved_credits) == 0);
		write_lock(&journal->j_state_lock);
	}

	/* Wait until there are no running updates */
	while (1) {
		transaction_t *transaction = journal->j_running_transaction;

		if (!transaction)
			break;

		spin_lock(&transaction->t_handle_lock);
		prepare_to_wait(&journal->j_wait_updates, &wait,
				TASK_UNINTERRUPTIBLE);
		if (!atomic_read(&transaction->t_updates)) {
			spin_unlock(&transaction->t_handle_lock);
			finish_wait(&journal->j_wait_updates, &wait);
			break;
		}
		spin_unlock(&transaction->t_handle_lock);
		write_unlock(&journal->j_state_lock);
		schedule();
		finish_wait(&journal->j_wait_updates, &wait);
		write_lock(&journal->j_state_lock);
	}
	write_unlock(&journal->j_state_lock);

	/*
	 * We have now established a barrier against other normal updates, but
	 * we also need to barrier against other jbd2_journal_lock_updates() calls
	 * to make sure that we serialise special journal-locked operations
	 * too.
	 */
	mutex_lock(&journal->j_barrier);
}

/**
 * void jbd2_journal_unlock_updates (journal_t* journal) - release barrier
 * @journal:  Journal to release the barrier on.
 *
 * Release a transaction barrier obtained with jbd2_journal_lock_updates().
 *
 * Should be called without the journal lock held.
 */
void jbd2_journal_unlock_updates (journal_t *journal)
{
	J_ASSERT(journal->j_barrier_count != 0);

	mutex_unlock(&journal->j_barrier);
	write_lock(&journal->j_state_lock);
	--journal->j_barrier_count;
	write_unlock(&journal->j_state_lock);
	wake_up(&journal->j_wait_transaction_locked);
}

static void warn_dirty_buffer(struct buffer_head *bh)
{
	printk(KERN_WARNING
	       "JBD2: Spotted dirty metadata buffer (dev = %pg, blocknr = %llu). "
	       "There's a risk of filesystem corruption in case of system "
	       "crash.\n",
	       bh->b_bdev, (unsigned long long)bh->b_blocknr);
}

/* Call t_frozen trigger and copy buffer data into jh->b_frozen_data. */
static void jbd2_freeze_jh_data(struct journal_head *jh)
{
	struct page *page;
	int offset;
	char *source;
	struct buffer_head *bh = jh2bh(jh);

	J_EXPECT_JH(jh, buffer_uptodate(bh), "Possible IO failure.\n");
	page = bh->b_page;
	offset = offset_in_page(bh->b_data);
	source = kmap_atomic(page);
	/* Fire data frozen trigger just before we copy the data */
	jbd2_buffer_frozen_trigger(jh, source + offset, jh->b_triggers);
	memcpy(jh->b_frozen_data, source + offset, bh->b_size);
	kunmap_atomic(source);

	/*
	 * Now that the frozen data is saved off, we need to store any matching
	 * triggers.
	 */
	jh->b_frozen_triggers = jh->b_triggers;
}

/*
 * If the buffer is already part of the current transaction, then there
 * is nothing we need to do.  If it is already part of a prior
 * transaction which we are still committing to disk, then we need to
 * make sure that we do not overwrite the old copy: we do copy-out to
 * preserve the copy going to disk.  We also account the buffer against
 * the handle's metadata buffer credits (unless the buffer is already
 * part of the transaction, that is).
 *
 */
static int
do_get_write_access(handle_t *handle, struct journal_head *jh,
			int force_copy)
{
	struct buffer_head *bh;
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal;
	int error;
	char *frozen_buffer = NULL;
	unsigned long start_lock, time_lock;

	journal = transaction->t_journal;

	jbd_debug(5, "journal_head %p, force_copy %d\n", jh, force_copy);

	JBUFFER_TRACE(jh, "entry");
repeat:
	bh = jh2bh(jh);

	/* @@@ Need to check for errors here at some point. */

 	start_lock = jiffies;
	lock_buffer(bh);
	spin_lock(&jh->b_state_lock);

	/* If it takes too long to lock the buffer, trace it */
	time_lock = jbd2_time_diff(start_lock, jiffies);
	if (time_lock > HZ/10)
		trace_jbd2_lock_buffer_stall(bh->b_bdev->bd_dev,
			jiffies_to_msecs(time_lock));

	/* We now hold the buffer lock so it is safe to query the buffer
	 * state.  Is the buffer dirty?
	 *
	 * If so, there are two possibilities.  The buffer may be
	 * non-journaled, and undergoing a quite legitimate writeback.
	 * Otherwise, it is journaled, and we don't expect dirty buffers
	 * in that state (the buffers should be marked JBD_Dirty
	 * instead.)  So either the IO is being done under our own
	 * control and this is a bug, or it's a third party IO such as
	 * dump(8) (which may leave the buffer scheduled for read ---
	 * ie. locked but not dirty) or tune2fs (which may actually have
	 * the buffer dirtied, ugh.)  */

	if (buffer_dirty(bh)) {
		/*
		 * First question: is this buffer already part of the current
		 * transaction or the existing committing transaction?
		 */
		if (jh->b_transaction) {
			J_ASSERT_JH(jh,
				jh->b_transaction == transaction ||
				jh->b_transaction ==
					journal->j_committing_transaction);
			if (jh->b_next_transaction)
				J_ASSERT_JH(jh, jh->b_next_transaction ==
							transaction);
			warn_dirty_buffer(bh);
		}
		/*
		 * In any case we need to clean the dirty flag and we must
		 * do it under the buffer lock to be sure we don't race
		 * with running write-out.
		 */
		JBUFFER_TRACE(jh, "Journalling dirty buffer");
		clear_buffer_dirty(bh);
		set_buffer_jbddirty(bh);
	}

	unlock_buffer(bh);

	error = -EROFS;
	if (is_handle_aborted(handle)) {
		spin_unlock(&jh->b_state_lock);
		goto out;
	}
	error = 0;

	/*
	 * The buffer is already part of this transaction if b_transaction or
	 * b_next_transaction points to it
	 */
	if (jh->b_transaction == transaction ||
	    jh->b_next_transaction == transaction)
		goto done;

	/*
	 * this is the first time this transaction is touching this buffer,
	 * reset the modified flag
	 */
	jh->b_modified = 0;

	/*
	 * If the buffer is not journaled right now, we need to make sure it
	 * doesn't get written to disk before the caller actually commits the
	 * new data
	 */
	if (!jh->b_transaction) {
		JBUFFER_TRACE(jh, "no transaction");
		J_ASSERT_JH(jh, !jh->b_next_transaction);
		JBUFFER_TRACE(jh, "file as BJ_Reserved");
		/*
		 * Make sure all stores to jh (b_modified, b_frozen_data) are
		 * visible before attaching it to the running transaction.
		 * Paired with barrier in jbd2_write_access_granted()
		 */
		smp_wmb();
		spin_lock(&journal->j_list_lock);
		__jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
		spin_unlock(&journal->j_list_lock);
		goto done;
	}
	/*
	 * If there is already a copy-out version of this buffer, then we don't
	 * need to make another one
	 */
	if (jh->b_frozen_data) {
		JBUFFER_TRACE(jh, "has frozen data");
		J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
		goto attach_next;
	}

	JBUFFER_TRACE(jh, "owned by older transaction");
	J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
	J_ASSERT_JH(jh, jh->b_transaction == journal->j_committing_transaction);

	/*
	 * There is one case we have to be very careful about.  If the
	 * committing transaction is currently writing this buffer out to disk
	 * and has NOT made a copy-out, then we cannot modify the buffer
	 * contents at all right now.  The essence of copy-out is that it is
	 * the extra copy, not the primary copy, which gets journaled.  If the
	 * primary copy is already going to disk then we cannot do copy-out
	 * here.
	 */
	if (buffer_shadow(bh)) {
		JBUFFER_TRACE(jh, "on shadow: sleep");
		spin_unlock(&jh->b_state_lock);
		wait_on_bit_io(&bh->b_state, BH_Shadow, TASK_UNINTERRUPTIBLE);
		goto repeat;
	}

	/*
	 * Only do the copy if the currently-owning transaction still needs it.
	 * If buffer isn't on BJ_Metadata list, the committing transaction is
	 * past that stage (here we use the fact that BH_Shadow is set under
	 * bh_state lock together with refiling to BJ_Shadow list and at this
	 * point we know the buffer doesn't have BH_Shadow set).
	 *
	 * Subtle point, though: if this is a get_undo_access, then we will be
	 * relying on the frozen_data to contain the new value of the
	 * committed_data record after the transaction, so we HAVE to force the
	 * frozen_data copy in that case.
	 */
	if (jh->b_jlist == BJ_Metadata || force_copy) {
		JBUFFER_TRACE(jh, "generate frozen data");
		if (!frozen_buffer) {
			JBUFFER_TRACE(jh, "allocate memory for buffer");
			spin_unlock(&jh->b_state_lock);
			frozen_buffer = jbd2_alloc(jh2bh(jh)->b_size,
						   GFP_NOFS | __GFP_NOFAIL);
			goto repeat;
		}
		jh->b_frozen_data = frozen_buffer;
		frozen_buffer = NULL;
		jbd2_freeze_jh_data(jh);
	}
attach_next:
	/*
	 * Make sure all stores to jh (b_modified, b_frozen_data) are visible
	 * before attaching it to the running transaction. Paired with barrier
	 * in jbd2_write_access_granted()
	 */
	smp_wmb();
	jh->b_next_transaction = transaction;

done:
	spin_unlock(&jh->b_state_lock);

	/*
	 * If we are about to journal a buffer, then any revoke pending on it is
	 * no longer valid
	 */
	jbd2_journal_cancel_revoke(handle, jh);

out:
	if (unlikely(frozen_buffer))	/* It's usually NULL */
		jbd2_free(frozen_buffer, bh->b_size);

	JBUFFER_TRACE(jh, "exit");
	return error;
}

/* Fast check whether buffer is already attached to the required transaction */
static bool jbd2_write_access_granted(handle_t *handle, struct buffer_head *bh,
							bool undo)
{
	struct journal_head *jh;
	bool ret = false;

	/* Dirty buffers require special handling... */
	if (buffer_dirty(bh))
		return false;

	/*
	 * RCU protects us from dereferencing freed pages. So the checks we do
	 * are guaranteed not to oops. However the jh slab object can get freed
	 * & reallocated while we work with it. So we have to be careful. When
	 * we see jh attached to the running transaction, we know it must stay
	 * so until the transaction is committed. Thus jh won't be freed and
	 * will be attached to the same bh while we run.  However it can
	 * happen jh gets freed, reallocated, and attached to the transaction
	 * just after we get pointer to it from bh. So we have to be careful
	 * and recheck jh still belongs to our bh before we return success.
	 */
	rcu_read_lock();
	if (!buffer_jbd(bh))
		goto out;
	/* This should be bh2jh() but that doesn't work with inline functions */
	jh = READ_ONCE(bh->b_private);
	if (!jh)
		goto out;
	/* For undo access buffer must have data copied */
	if (undo && !jh->b_committed_data)
		goto out;
	if (READ_ONCE(jh->b_transaction) != handle->h_transaction &&
	    READ_ONCE(jh->b_next_transaction) != handle->h_transaction)
		goto out;
	/*
	 * There are two reasons for the barrier here:
	 * 1) Make sure to fetch b_bh after we did previous checks so that we
	 * detect when jh went through free, realloc, attach to transaction
	 * while we were checking. Paired with implicit barrier in that path.
	 * 2) So that access to bh done after jbd2_write_access_granted()
	 * doesn't get reordered and see inconsistent state of concurrent
	 * do_get_write_access().
	 */
	smp_mb();
	if (unlikely(jh->b_bh != bh))
		goto out;
	ret = true;
out:
	rcu_read_unlock();
	return ret;
}

/**
 * int jbd2_journal_get_write_access() - notify intent to modify a buffer for metadata (not data) update.
 * @handle: transaction to add buffer modifications to
 * @bh:     bh to be used for metadata writes
 *
 * Returns: error code or 0 on success.
 *
 * In full data journalling mode the buffer may be of type BJ_AsyncData,
 * because we're ``write()ing`` a buffer which is also part of a shared mapping.
 */

int jbd2_journal_get_write_access(handle_t *handle, struct buffer_head *bh)
{
	struct journal_head *jh;
	int rc;

	if (is_handle_aborted(handle))
		return -EROFS;

	if (jbd2_write_access_granted(handle, bh, false))
		return 0;

	jh = jbd2_journal_add_journal_head(bh);
	/* We do not want to get caught playing with fields which the
	 * log thread also manipulates.  Make sure that the buffer
	 * completes any outstanding IO before proceeding. */
	rc = do_get_write_access(handle, jh, 0);
	jbd2_journal_put_journal_head(jh);
	return rc;
}


/*
 * When the user wants to journal a newly created buffer_head
 * (ie. getblk() returned a new buffer and we are going to populate it
 * manually rather than reading off disk), then we need to keep the
 * buffer_head locked until it has been completely filled with new
 * data.  In this case, we should be able to make the assertion that
 * the bh is not already part of an existing transaction.
 *
 * The buffer should already be locked by the caller by this point.
 * There is no lock ranking violation: it was a newly created,
 * unlocked buffer beforehand. */

/**
 * int jbd2_journal_get_create_access () - notify intent to use newly created bh
 * @handle: transaction to new buffer to
 * @bh: new buffer.
 *
 * Call this if you create a new bh.
 */
int jbd2_journal_get_create_access(handle_t *handle, struct buffer_head *bh)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal;
	struct journal_head *jh = jbd2_journal_add_journal_head(bh);
	int err;

	jbd_debug(5, "journal_head %p\n", jh);
	err = -EROFS;
	if (is_handle_aborted(handle))
		goto out;
	journal = transaction->t_journal;
	err = 0;

	JBUFFER_TRACE(jh, "entry");
	/*
	 * The buffer may already belong to this transaction due to pre-zeroing
	 * in the filesystem's new_block code.  It may also be on the previous,
	 * committing transaction's lists, but it HAS to be in Forget state in
	 * that case: the transaction must have deleted the buffer for it to be
	 * reused here.
	 */
	spin_lock(&jh->b_state_lock);
	J_ASSERT_JH(jh, (jh->b_transaction == transaction ||
		jh->b_transaction == NULL ||
		(jh->b_transaction == journal->j_committing_transaction &&
			  jh->b_jlist == BJ_Forget)));

	J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
	J_ASSERT_JH(jh, buffer_locked(jh2bh(jh)));

	if (jh->b_transaction == NULL) {
		/*
		 * Previous jbd2_journal_forget() could have left the buffer
		 * with jbddirty bit set because it was being committed. When
		 * the commit finished, we've filed the buffer for
		 * checkpointing and marked it dirty. Now we are reallocating
		 * the buffer so the transaction freeing it must have
		 * committed and so it's safe to clear the dirty bit.
		 */
		clear_buffer_dirty(jh2bh(jh));
		/* first access by this transaction */
		jh->b_modified = 0;

		JBUFFER_TRACE(jh, "file as BJ_Reserved");
		spin_lock(&journal->j_list_lock);
		__jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
		spin_unlock(&journal->j_list_lock);
	} else if (jh->b_transaction == journal->j_committing_transaction) {
		/* first access by this transaction */
		jh->b_modified = 0;

		JBUFFER_TRACE(jh, "set next transaction");
		spin_lock(&journal->j_list_lock);
		jh->b_next_transaction = transaction;
		spin_unlock(&journal->j_list_lock);
	}
	spin_unlock(&jh->b_state_lock);

	/*
	 * akpm: I added this.  ext3_alloc_branch can pick up new indirect
	 * blocks which contain freed but then revoked metadata.  We need
	 * to cancel the revoke in case we end up freeing it yet again
	 * and the reallocating as data - this would cause a second revoke,
	 * which hits an assertion error.
	 */
	JBUFFER_TRACE(jh, "cancelling revoke");
	jbd2_journal_cancel_revoke(handle, jh);
out:
	jbd2_journal_put_journal_head(jh);
	return err;
}

/**
 * int jbd2_journal_get_undo_access() -  Notify intent to modify metadata with
 *     non-rewindable consequences
 * @handle: transaction
 * @bh: buffer to undo
 *
 * Sometimes there is a need to distinguish between metadata which has
 * been committed to disk and that which has not.  The ext3fs code uses
 * this for freeing and allocating space, we have to make sure that we
 * do not reuse freed space until the deallocation has been committed,
 * since if we overwrote that space we would make the delete
 * un-rewindable in case of a crash.
 *
 * To deal with that, jbd2_journal_get_undo_access requests write access to a
 * buffer for parts of non-rewindable operations such as delete
 * operations on the bitmaps.  The journaling code must keep a copy of
 * the buffer's contents prior to the undo_access call until such time
 * as we know that the buffer has definitely been committed to disk.
 *
 * We never need to know which transaction the committed data is part
 * of, buffers touched here are guaranteed to be dirtied later and so
 * will be committed to a new transaction in due course, at which point
 * we can discard the old committed data pointer.
 *
 * Returns error number or 0 on success.
 */
int jbd2_journal_get_undo_access(handle_t *handle, struct buffer_head *bh)
{
	int err;
	struct journal_head *jh;
	char *committed_data = NULL;

	if (is_handle_aborted(handle))
		return -EROFS;

	if (jbd2_write_access_granted(handle, bh, true))
		return 0;

	jh = jbd2_journal_add_journal_head(bh);
	JBUFFER_TRACE(jh, "entry");

	/*
	 * Do this first --- it can drop the journal lock, so we want to
	 * make sure that obtaining the committed_data is done
	 * atomically wrt. completion of any outstanding commits.
	 */
	err = do_get_write_access(handle, jh, 1);
	if (err)
		goto out;

repeat:
	if (!jh->b_committed_data)
		committed_data = jbd2_alloc(jh2bh(jh)->b_size,
					    GFP_NOFS|__GFP_NOFAIL);

	spin_lock(&jh->b_state_lock);
	if (!jh->b_committed_data) {
		/* Copy out the current buffer contents into the
		 * preserved, committed copy. */
		JBUFFER_TRACE(jh, "generate b_committed data");
		if (!committed_data) {
			spin_unlock(&jh->b_state_lock);
			goto repeat;
		}

		jh->b_committed_data = committed_data;
		committed_data = NULL;
		memcpy(jh->b_committed_data, bh->b_data, bh->b_size);
	}
	spin_unlock(&jh->b_state_lock);
out:
	jbd2_journal_put_journal_head(jh);
	if (unlikely(committed_data))
		jbd2_free(committed_data, bh->b_size);
	return err;
}

/**
 * void jbd2_journal_set_triggers() - Add triggers for commit writeout
 * @bh: buffer to trigger on
 * @type: struct jbd2_buffer_trigger_type containing the trigger(s).
 *
 * Set any triggers on this journal_head.  This is always safe, because
 * triggers for a committing buffer will be saved off, and triggers for
 * a running transaction will match the buffer in that transaction.
 *
 * Call with NULL to clear the triggers.
 */
void jbd2_journal_set_triggers(struct buffer_head *bh,
			       struct jbd2_buffer_trigger_type *type)
{
	struct journal_head *jh = jbd2_journal_grab_journal_head(bh);

	if (WARN_ON(!jh))
		return;
	jh->b_triggers = type;
	jbd2_journal_put_journal_head(jh);
}

void jbd2_buffer_frozen_trigger(struct journal_head *jh, void *mapped_data,
				struct jbd2_buffer_trigger_type *triggers)
{
	struct buffer_head *bh = jh2bh(jh);

	if (!triggers || !triggers->t_frozen)
		return;

	triggers->t_frozen(triggers, bh, mapped_data, bh->b_size);
}

void jbd2_buffer_abort_trigger(struct journal_head *jh,
			       struct jbd2_buffer_trigger_type *triggers)
{
	if (!triggers || !triggers->t_abort)
		return;

	triggers->t_abort(triggers, jh2bh(jh));
}

/**
 * int jbd2_journal_dirty_metadata() -  mark a buffer as containing dirty metadata
 * @handle: transaction to add buffer to.
 * @bh: buffer to mark
 *
 * mark dirty metadata which needs to be journaled as part of the current
 * transaction.
 *
 * The buffer must have previously had jbd2_journal_get_write_access()
 * called so that it has a valid journal_head attached to the buffer
 * head.
 *
 * The buffer is placed on the transaction's metadata list and is marked
 * as belonging to the transaction.
 *
 * Returns error number or 0 on success.
 *
 * Special care needs to be taken if the buffer already belongs to the
 * current committing transaction (in which case we should have frozen
 * data present for that commit).  In that case, we don't relink the
 * buffer: that only gets done when the old transaction finally
 * completes its commit.
 */
int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal;
	struct journal_head *jh;
	int ret = 0;

	if (is_handle_aborted(handle))
		return -EROFS;
	if (!buffer_jbd(bh))
		return -EUCLEAN;

	/*
	 * We don't grab jh reference here since the buffer must be part
	 * of the running transaction.
	 */
	jh = bh2jh(bh);
	jbd_debug(5, "journal_head %p\n", jh);
	JBUFFER_TRACE(jh, "entry");

	/*
	 * This and the following assertions are unreliable since we may see jh
	 * in inconsistent state unless we grab bh_state lock. But this is
	 * crucial to catch bugs so let's do a reliable check until the
	 * lockless handling is fully proven.
	 */
	if (jh->b_transaction != transaction &&
	    jh->b_next_transaction != transaction) {
		spin_lock(&jh->b_state_lock);
		J_ASSERT_JH(jh, jh->b_transaction == transaction ||
				jh->b_next_transaction == transaction);
		spin_unlock(&jh->b_state_lock);
	}
	if (jh->b_modified == 1) {
		/* If it's in our transaction it must be in BJ_Metadata list. */
		if (jh->b_transaction == transaction &&
		    jh->b_jlist != BJ_Metadata) {
			spin_lock(&jh->b_state_lock);
			if (jh->b_transaction == transaction &&
			    jh->b_jlist != BJ_Metadata)
				pr_err("JBD2: assertion failure: h_type=%u "
				       "h_line_no=%u block_no=%llu jlist=%u\n",
				       handle->h_type, handle->h_line_no,
				       (unsigned long long) bh->b_blocknr,
				       jh->b_jlist);
			J_ASSERT_JH(jh, jh->b_transaction != transaction ||
					jh->b_jlist == BJ_Metadata);
			spin_unlock(&jh->b_state_lock);
		}
		goto out;
	}

	journal = transaction->t_journal;
	spin_lock(&jh->b_state_lock);

	if (jh->b_modified == 0) {
		/*
		 * This buffer's got modified and becoming part
		 * of the transaction. This needs to be done
		 * once a transaction -bzzz
		 */
		if (WARN_ON_ONCE(jbd2_handle_buffer_credits(handle) <= 0)) {
			ret = -ENOSPC;
			goto out_unlock_bh;
		}
		jh->b_modified = 1;
		handle->h_total_credits--;
	}

	/*
	 * fastpath, to avoid expensive locking.  If this buffer is already
	 * on the running transaction's metadata list there is nothing to do.
	 * Nobody can take it off again because there is a handle open.
	 * I _think_ we're OK here with SMP barriers - a mistaken decision will
	 * result in this test being false, so we go in and take the locks.
	 */
	if (jh->b_transaction == transaction && jh->b_jlist == BJ_Metadata) {
		JBUFFER_TRACE(jh, "fastpath");
		if (unlikely(jh->b_transaction !=
			     journal->j_running_transaction)) {
			printk(KERN_ERR "JBD2: %s: "
			       "jh->b_transaction (%llu, %p, %u) != "
			       "journal->j_running_transaction (%p, %u)\n",
			       journal->j_devname,
			       (unsigned long long) bh->b_blocknr,
			       jh->b_transaction,
			       jh->b_transaction ? jh->b_transaction->t_tid : 0,
			       journal->j_running_transaction,
			       journal->j_running_transaction ?
			       journal->j_running_transaction->t_tid : 0);
			ret = -EINVAL;
		}
		goto out_unlock_bh;
	}

	set_buffer_jbddirty(bh);

	/*
	 * Metadata already on the current transaction list doesn't
	 * need to be filed.  Metadata on another transaction's list must
	 * be committing, and will be refiled once the commit completes:
	 * leave it alone for now.
	 */
	if (jh->b_transaction != transaction) {
		JBUFFER_TRACE(jh, "already on other transaction");
		if (unlikely(((jh->b_transaction !=
			       journal->j_committing_transaction)) ||
			     (jh->b_next_transaction != transaction))) {
			printk(KERN_ERR "jbd2_journal_dirty_metadata: %s: "
			       "bad jh for block %llu: "
			       "transaction (%p, %u), "
			       "jh->b_transaction (%p, %u), "
			       "jh->b_next_transaction (%p, %u), jlist %u\n",
			       journal->j_devname,
			       (unsigned long long) bh->b_blocknr,
			       transaction, transaction->t_tid,
			       jh->b_transaction,
			       jh->b_transaction ?
			       jh->b_transaction->t_tid : 0,
			       jh->b_next_transaction,
			       jh->b_next_transaction ?
			       jh->b_next_transaction->t_tid : 0,
			       jh->b_jlist);
			WARN_ON(1);
			ret = -EINVAL;
		}
		/* And this case is illegal: we can't reuse another
		 * transaction's data buffer, ever. */
		goto out_unlock_bh;
	}

	/* That test should have eliminated the following case: */
	J_ASSERT_JH(jh, jh->b_frozen_data == NULL);

	JBUFFER_TRACE(jh, "file as BJ_Metadata");
	spin_lock(&journal->j_list_lock);
	__jbd2_journal_file_buffer(jh, transaction, BJ_Metadata);
	spin_unlock(&journal->j_list_lock);
out_unlock_bh:
	spin_unlock(&jh->b_state_lock);
out:
	JBUFFER_TRACE(jh, "exit");
	return ret;
}

/**
 * void jbd2_journal_forget() - bforget() for potentially-journaled buffers.
 * @handle: transaction handle
 * @bh:     bh to 'forget'
 *
 * We can only do the bforget if there are no commits pending against the
 * buffer.  If the buffer is dirty in the current running transaction we
 * can safely unlink it.
 *
 * bh may not be a journalled buffer at all - it may be a non-JBD
 * buffer which came off the hashtable.  Check for this.
 *
 * Decrements bh->b_count by one.
 *
 * Allow this call even if the handle has aborted --- it may be part of
 * the caller's cleanup after an abort.
 */
int jbd2_journal_forget(handle_t *handle, struct buffer_head *bh)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal;
	struct journal_head *jh;
	int drop_reserve = 0;
	int err = 0;
	int was_modified = 0;

	if (is_handle_aborted(handle))
		return -EROFS;
	journal = transaction->t_journal;

	BUFFER_TRACE(bh, "entry");

	jh = jbd2_journal_grab_journal_head(bh);
	if (!jh) {
		__bforget(bh);
		return 0;
	}

	spin_lock(&jh->b_state_lock);

	/* Critical error: attempting to delete a bitmap buffer, maybe?
	 * Don't do any jbd operations, and return an error. */
	if (!J_EXPECT_JH(jh, !jh->b_committed_data,
			 "inconsistent data on disk")) {
		err = -EIO;
		goto drop;
	}

	/* keep track of whether or not this transaction modified us */
	was_modified = jh->b_modified;

	/*
	 * The buffer's going from the transaction, we must drop
	 * all references -bzzz
	 */
	jh->b_modified = 0;

	if (jh->b_transaction == transaction) {
		J_ASSERT_JH(jh, !jh->b_frozen_data);

		/* If we are forgetting a buffer which is already part
		 * of this transaction, then we can just drop it from
		 * the transaction immediately. */
		clear_buffer_dirty(bh);
		clear_buffer_jbddirty(bh);

		JBUFFER_TRACE(jh, "belongs to current transaction: unfile");

		/*
		 * we only want to drop a reference if this transaction
		 * modified the buffer
		 */
		if (was_modified)
			drop_reserve = 1;

		/*
		 * We are no longer going to journal this buffer.
		 * However, the commit of this transaction is still
		 * important to the buffer: the delete that we are now
		 * processing might obsolete an old log entry, so by
		 * committing, we can satisfy the buffer's checkpoint.
		 *
		 * So, if we have a checkpoint on the buffer, we should
		 * now refile the buffer on our BJ_Forget list so that
		 * we know to remove the checkpoint after we commit.
		 */

		spin_lock(&journal->j_list_lock);
		if (jh->b_cp_transaction) {
			__jbd2_journal_temp_unlink_buffer(jh);
			__jbd2_journal_file_buffer(jh, transaction, BJ_Forget);
		} else {
			__jbd2_journal_unfile_buffer(jh);
			jbd2_journal_put_journal_head(jh);
		}
		spin_unlock(&journal->j_list_lock);
	} else if (jh->b_transaction) {
		J_ASSERT_JH(jh, (jh->b_transaction ==
				 journal->j_committing_transaction));
		/* However, if the buffer is still owned by a prior
		 * (committing) transaction, we can't drop it yet... */
		JBUFFER_TRACE(jh, "belongs to older transaction");
		/* ... but we CAN drop it from the new transaction through
		 * marking the buffer as freed and set j_next_transaction to
		 * the new transaction, so that not only the commit code
		 * knows it should clear dirty bits when it is done with the
		 * buffer, but also the buffer can be checkpointed only
		 * after the new transaction commits. */

		set_buffer_freed(bh);

		if (!jh->b_next_transaction) {
			spin_lock(&journal->j_list_lock);
			jh->b_next_transaction = transaction;
			spin_unlock(&journal->j_list_lock);
		} else {
			J_ASSERT(jh->b_next_transaction == transaction);

			/*
			 * only drop a reference if this transaction modified
			 * the buffer
			 */
			if (was_modified)
				drop_reserve = 1;
		}
	} else {
		/*
		 * Finally, if the buffer is not belongs to any
		 * transaction, we can just drop it now if it has no
		 * checkpoint.
		 */
		spin_lock(&journal->j_list_lock);
		if (!jh->b_cp_transaction) {
			JBUFFER_TRACE(jh, "belongs to none transaction");
			spin_unlock(&journal->j_list_lock);
			goto drop;
		}

		/*
		 * Otherwise, if the buffer has been written to disk,
		 * it is safe to remove the checkpoint and drop it.
		 */
		if (!buffer_dirty(bh)) {
			__jbd2_journal_remove_checkpoint(jh);
			spin_unlock(&journal->j_list_lock);
			goto drop;
		}

		/*
		 * The buffer is still not written to disk, we should
		 * attach this buffer to current transaction so that the
		 * buffer can be checkpointed only after the current
		 * transaction commits.
		 */
		clear_buffer_dirty(bh);
		__jbd2_journal_file_buffer(jh, transaction, BJ_Forget);
		spin_unlock(&journal->j_list_lock);
	}
drop:
	__brelse(bh);
	spin_unlock(&jh->b_state_lock);
	jbd2_journal_put_journal_head(jh);
	if (drop_reserve) {
		/* no need to reserve log space for this block -bzzz */
		handle->h_total_credits++;
	}
	return err;
}

/**
 * int jbd2_journal_stop() - complete a transaction
 * @handle: transaction to complete.
 *
 * All done for a particular handle.
 *
 * There is not much action needed here.  We just return any remaining
 * buffer credits to the transaction and remove the handle.  The only
 * complication is that we need to start a commit operation if the
 * filesystem is marked for synchronous update.
 *
 * jbd2_journal_stop itself will not usually return an error, but it may
 * do so in unusual circumstances.  In particular, expect it to
 * return -EIO if a jbd2_journal_abort has been executed since the
 * transaction began.
 */
int jbd2_journal_stop(handle_t *handle)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal;
	int err = 0, wait_for_commit = 0;
	tid_t tid;
	pid_t pid;

	if (--handle->h_ref > 0) {
		jbd_debug(4, "h_ref %d -> %d\n", handle->h_ref + 1,
						 handle->h_ref);
		if (is_handle_aborted(handle))
			return -EIO;
		return 0;
	}
	if (!transaction) {
		/*
		 * Handle is already detached from the transaction so there is
		 * nothing to do other than free the handle.
		 */
		memalloc_nofs_restore(handle->saved_alloc_context);
		goto free_and_exit;
	}
	journal = transaction->t_journal;
	tid = transaction->t_tid;

	if (is_handle_aborted(handle))
		err = -EIO;

	jbd_debug(4, "Handle %p going down\n", handle);
	trace_jbd2_handle_stats(journal->j_fs_dev->bd_dev,
				tid, handle->h_type, handle->h_line_no,
				jiffies - handle->h_start_jiffies,
				handle->h_sync, handle->h_requested_credits,
				(handle->h_requested_credits -
				 handle->h_total_credits));

	/*
	 * Implement synchronous transaction batching.  If the handle
	 * was synchronous, don't force a commit immediately.  Let's
	 * yield and let another thread piggyback onto this
	 * transaction.  Keep doing that while new threads continue to
	 * arrive.  It doesn't cost much - we're about to run a commit
	 * and sleep on IO anyway.  Speeds up many-threaded, many-dir
	 * operations by 30x or more...
	 *
	 * We try and optimize the sleep time against what the
	 * underlying disk can do, instead of having a static sleep
	 * time.  This is useful for the case where our storage is so
	 * fast that it is more optimal to go ahead and force a flush
	 * and wait for the transaction to be committed than it is to
	 * wait for an arbitrary amount of time for new writers to
	 * join the transaction.  We achieve this by measuring how
	 * long it takes to commit a transaction, and compare it with
	 * how long this transaction has been running, and if run time
	 * < commit time then we sleep for the delta and commit.  This
	 * greatly helps super fast disks that would see slowdowns as
	 * more threads started doing fsyncs.
	 *
	 * But don't do this if this process was the most recent one
	 * to perform a synchronous write.  We do this to detect the
	 * case where a single process is doing a stream of sync
	 * writes.  No point in waiting for joiners in that case.
	 *
	 * Setting max_batch_time to 0 disables this completely.
	 */
	pid = current->pid;
	if (handle->h_sync && journal->j_last_sync_writer != pid &&
	    journal->j_max_batch_time) {
		u64 commit_time, trans_time;

		journal->j_last_sync_writer = pid;

		read_lock(&journal->j_state_lock);
		commit_time = journal->j_average_commit_time;
		read_unlock(&journal->j_state_lock);

		trans_time = ktime_to_ns(ktime_sub(ktime_get(),
						   transaction->t_start_time));

		commit_time = max_t(u64, commit_time,
				    1000*journal->j_min_batch_time);
		commit_time = min_t(u64, commit_time,
				    1000*journal->j_max_batch_time);

		if (trans_time < commit_time) {
			ktime_t expires = ktime_add_ns(ktime_get(),
						       commit_time);
			set_current_state(TASK_UNINTERRUPTIBLE);
			schedule_hrtimeout(&expires, HRTIMER_MODE_ABS);
		}
	}

	if (handle->h_sync)
		transaction->t_synchronous_commit = 1;

	/*
	 * If the handle is marked SYNC, we need to set another commit
	 * going!  We also want to force a commit if the transaction is too
	 * old now.
	 */
	if (handle->h_sync ||
	    time_after_eq(jiffies, transaction->t_expires)) {
		/* Do this even for aborted journals: an abort still
		 * completes the commit thread, it just doesn't write
		 * anything to disk. */

		jbd_debug(2, "transaction too old, requesting commit for "
					"handle %p\n", handle);
		/* This is non-blocking */
		jbd2_log_start_commit(journal, tid);

		/*
		 * Special case: JBD2_SYNC synchronous updates require us
		 * to wait for the commit to complete.
		 */
		if (handle->h_sync && !(current->flags & PF_MEMALLOC))
			wait_for_commit = 1;
	}

	/*
	 * Once stop_this_handle() drops t_updates, the transaction could start
	 * committing on us and eventually disappear.  So we must not
	 * dereference transaction pointer again after calling
	 * stop_this_handle().
	 */
	stop_this_handle(handle);

	if (wait_for_commit)
		err = jbd2_log_wait_commit(journal, tid);

free_and_exit:
	if (handle->h_rsv_handle)
		jbd2_free_handle(handle->h_rsv_handle);
	jbd2_free_handle(handle);
	return err;
}

/*
 *
 * List management code snippets: various functions for manipulating the
 * transaction buffer lists.
 *
 */

/*
 * Append a buffer to a transaction list, given the transaction's list head
 * pointer.
 *
 * j_list_lock is held.
 *
 * jh->b_state_lock is held.
 */

static inline void
__blist_add_buffer(struct journal_head **list, struct journal_head *jh)
{
	if (!*list) {
		jh->b_tnext = jh->b_tprev = jh;
		*list = jh;
	} else {
		/* Insert at the tail of the list to preserve order */
		struct journal_head *first = *list, *last = first->b_tprev;
		jh->b_tprev = last;
		jh->b_tnext = first;
		last->b_tnext = first->b_tprev = jh;
	}
}

/*
 * Remove a buffer from a transaction list, given the transaction's list
 * head pointer.
 *
 * Called with j_list_lock held, and the journal may not be locked.
 *
 * jh->b_state_lock is held.
 */

static inline void
__blist_del_buffer(struct journal_head **list, struct journal_head *jh)
{
	if (*list == jh) {
		*list = jh->b_tnext;
		if (*list == jh)
			*list = NULL;
	}
	jh->b_tprev->b_tnext = jh->b_tnext;
	jh->b_tnext->b_tprev = jh->b_tprev;
}

/*
 * Remove a buffer from the appropriate transaction list.
 *
 * Note that this function can *change* the value of
 * bh->b_transaction->t_buffers, t_forget, t_shadow_list, t_log_list or
 * t_reserved_list.  If the caller is holding onto a copy of one of these
 * pointers, it could go bad.  Generally the caller needs to re-read the
 * pointer from the transaction_t.
 *
 * Called under j_list_lock.
 */
static void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh)
{
	struct journal_head **list = NULL;
	transaction_t *transaction;
	struct buffer_head *bh = jh2bh(jh);

	lockdep_assert_held(&jh->b_state_lock);
	transaction = jh->b_transaction;
	if (transaction)
		assert_spin_locked(&transaction->t_journal->j_list_lock);

	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
	if (jh->b_jlist != BJ_None)
		J_ASSERT_JH(jh, transaction != NULL);

	switch (jh->b_jlist) {
	case BJ_None:
		return;
	case BJ_Metadata:
		transaction->t_nr_buffers--;
		J_ASSERT_JH(jh, transaction->t_nr_buffers >= 0);
		list = &transaction->t_buffers;
		break;
	case BJ_Forget:
		list = &transaction->t_forget;
		break;
	case BJ_Shadow:
		list = &transaction->t_shadow_list;
		break;
	case BJ_Reserved:
		list = &transaction->t_reserved_list;
		break;
	}

	__blist_del_buffer(list, jh);
	jh->b_jlist = BJ_None;
	if (transaction && is_journal_aborted(transaction->t_journal))
		clear_buffer_jbddirty(bh);
	else if (test_clear_buffer_jbddirty(bh))
		mark_buffer_dirty(bh);	/* Expose it to the VM */
}

/*
 * Remove buffer from all transactions. The caller is responsible for dropping
 * the jh reference that belonged to the transaction.
 *
 * Called with bh_state lock and j_list_lock
 */
static void __jbd2_journal_unfile_buffer(struct journal_head *jh)
{
	J_ASSERT_JH(jh, jh->b_transaction != NULL);
	J_ASSERT_JH(jh, jh->b_next_transaction == NULL);

	__jbd2_journal_temp_unlink_buffer(jh);
	jh->b_transaction = NULL;
}

void jbd2_journal_unfile_buffer(journal_t *journal, struct journal_head *jh)
{
	struct buffer_head *bh = jh2bh(jh);

	/* Get reference so that buffer cannot be freed before we unlock it */
	get_bh(bh);
	spin_lock(&jh->b_state_lock);
	spin_lock(&journal->j_list_lock);
	__jbd2_journal_unfile_buffer(jh);
	spin_unlock(&journal->j_list_lock);
	spin_unlock(&jh->b_state_lock);
	jbd2_journal_put_journal_head(jh);
	__brelse(bh);
}

/*
 * Called from jbd2_journal_try_to_free_buffers().
 *
 * Called under jh->b_state_lock
 */
static void
__journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
{
	struct journal_head *jh;

	jh = bh2jh(bh);

	if (buffer_locked(bh) || buffer_dirty(bh))
		goto out;

	if (jh->b_next_transaction != NULL || jh->b_transaction != NULL)
		goto out;

	spin_lock(&journal->j_list_lock);
	if (jh->b_cp_transaction != NULL) {
		/* written-back checkpointed metadata buffer */
		JBUFFER_TRACE(jh, "remove from checkpoint list");
		__jbd2_journal_remove_checkpoint(jh);
	}
	spin_unlock(&journal->j_list_lock);
out:
	return;
}

/**
 * int jbd2_journal_try_to_free_buffers() - try to free page buffers.
 * @journal: journal for operation
 * @page: to try and free
 *
 * For all the buffers on this page,
 * if they are fully written out ordered data, move them onto BUF_CLEAN
 * so try_to_free_buffers() can reap them.
 *
 * This function returns non-zero if we wish try_to_free_buffers()
 * to be called. We do this if the page is releasable by try_to_free_buffers().
 * We also do it if the page has locked or dirty buffers and the caller wants
 * us to perform sync or async writeout.
 *
 * This complicates JBD locking somewhat.  We aren't protected by the
 * BKL here.  We wish to remove the buffer from its committing or
 * running transaction's ->t_datalist via __jbd2_journal_unfile_buffer.
 *
 * This may *change* the value of transaction_t->t_datalist, so anyone
 * who looks at t_datalist needs to lock against this function.
 *
 * Even worse, someone may be doing a jbd2_journal_dirty_data on this
 * buffer.  So we need to lock against that.  jbd2_journal_dirty_data()
 * will come out of the lock with the buffer dirty, which makes it
 * ineligible for release here.
 *
 * Who else is affected by this?  hmm...  Really the only contender
 * is do_get_write_access() - it could be looking at the buffer while
 * journal_try_to_free_buffer() is changing its state.  But that
 * cannot happen because we never reallocate freed data as metadata
 * while the data is part of a transaction.  Yes?
 *
 * Return 0 on failure, 1 on success
 */
int jbd2_journal_try_to_free_buffers(journal_t *journal, struct page *page)
{
	struct buffer_head *head;
	struct buffer_head *bh;
	bool has_write_io_error = false;
	int ret = 0;

	J_ASSERT(PageLocked(page));

	head = page_buffers(page);
	bh = head;
	do {
		struct journal_head *jh;

		/*
		 * We take our own ref against the journal_head here to avoid
		 * having to add tons of locking around each instance of
		 * jbd2_journal_put_journal_head().
		 */
		jh = jbd2_journal_grab_journal_head(bh);
		if (!jh)
			continue;

		spin_lock(&jh->b_state_lock);
		__journal_try_to_free_buffer(journal, bh);
		spin_unlock(&jh->b_state_lock);
		jbd2_journal_put_journal_head(jh);
		if (buffer_jbd(bh))
			goto busy;

		/*
		 * If we free a metadata buffer which has been failed to
		 * write out, the jbd2 checkpoint procedure will not detect
		 * this failure and may lead to filesystem inconsistency
		 * after cleanup journal tail.
		 */
		if (buffer_write_io_error(bh)) {
			pr_err("JBD2: Error while async write back metadata bh %llu.",
			       (unsigned long long)bh->b_blocknr);
			has_write_io_error = true;
		}
	} while ((bh = bh->b_this_page) != head);

	ret = try_to_free_buffers(page);

busy:
	if (has_write_io_error)
		jbd2_journal_abort(journal, -EIO);

	return ret;
}

/*
 * This buffer is no longer needed.  If it is on an older transaction's
 * checkpoint list we need to record it on this transaction's forget list
 * to pin this buffer (and hence its checkpointing transaction) down until
 * this transaction commits.  If the buffer isn't on a checkpoint list, we
 * release it.
 * Returns non-zero if JBD no longer has an interest in the buffer.
 *
 * Called under j_list_lock.
 *
 * Called under jh->b_state_lock.
 */
static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
{
	int may_free = 1;
	struct buffer_head *bh = jh2bh(jh);

	if (jh->b_cp_transaction) {
		JBUFFER_TRACE(jh, "on running+cp transaction");
		__jbd2_journal_temp_unlink_buffer(jh);
		/*
		 * We don't want to write the buffer anymore, clear the
		 * bit so that we don't confuse checks in
		 * __journal_file_buffer
		 */
		clear_buffer_dirty(bh);
		__jbd2_journal_file_buffer(jh, transaction, BJ_Forget);
		may_free = 0;
	} else {
		JBUFFER_TRACE(jh, "on running transaction");
		__jbd2_journal_unfile_buffer(jh);
		jbd2_journal_put_journal_head(jh);
	}
	return may_free;
}

/*
 * jbd2_journal_invalidatepage
 *
 * This code is tricky.  It has a number of cases to deal with.
 *
 * There are two invariants which this code relies on:
 *
 * i_size must be updated on disk before we start calling invalidatepage on the
 * data.
 *
 *  This is done in ext3 by defining an ext3_setattr method which
 *  updates i_size before truncate gets going.  By maintaining this
 *  invariant, we can be sure that it is safe to throw away any buffers
 *  attached to the current transaction: once the transaction commits,
 *  we know that the data will not be needed.
 *
 *  Note however that we can *not* throw away data belonging to the
 *  previous, committing transaction!
 *
 * Any disk blocks which *are* part of the previous, committing
 * transaction (and which therefore cannot be discarded immediately) are
 * not going to be reused in the new running transaction
 *
 *  The bitmap committed_data images guarantee this: any block which is
 *  allocated in one transaction and removed in the next will be marked
 *  as in-use in the committed_data bitmap, so cannot be reused until
 *  the next transaction to delete the block commits.  This means that
 *  leaving committing buffers dirty is quite safe: the disk blocks
 *  cannot be reallocated to a different file and so buffer aliasing is
 *  not possible.
 *
 *
 * The above applies mainly to ordered data mode.  In writeback mode we
 * don't make guarantees about the order in which data hits disk --- in
 * particular we don't guarantee that new dirty data is flushed before
 * transaction commit --- so it is always safe just to discard data
 * immediately in that mode.  --sct
 */

/*
 * The journal_unmap_buffer helper function returns zero if the buffer
 * concerned remains pinned as an anonymous buffer belonging to an older
 * transaction.
 *
 * We're outside-transaction here.  Either or both of j_running_transaction
 * and j_committing_transaction may be NULL.
 */
static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh,
				int partial_page)
{
	transaction_t *transaction;
	struct journal_head *jh;
	int may_free = 1;

	BUFFER_TRACE(bh, "entry");

	/*
	 * It is safe to proceed here without the j_list_lock because the
	 * buffers cannot be stolen by try_to_free_buffers as long as we are
	 * holding the page lock. --sct
	 */

	jh = jbd2_journal_grab_journal_head(bh);
	if (!jh)
		goto zap_buffer_unlocked;

	/* OK, we have data buffer in journaled mode */
	write_lock(&journal->j_state_lock);
	spin_lock(&jh->b_state_lock);
	spin_lock(&journal->j_list_lock);

	/*
	 * We cannot remove the buffer from checkpoint lists until the
	 * transaction adding inode to orphan list (let's call it T)
	 * is committed.  Otherwise if the transaction changing the
	 * buffer would be cleaned from the journal before T is
	 * committed, a crash will cause that the correct contents of
	 * the buffer will be lost.  On the other hand we have to
	 * clear the buffer dirty bit at latest at the moment when the
	 * transaction marking the buffer as freed in the filesystem
	 * structures is committed because from that moment on the
	 * block can be reallocated and used by a different page.
	 * Since the block hasn't been freed yet but the inode has
	 * already been added to orphan list, it is safe for us to add
	 * the buffer to BJ_Forget list of the newest transaction.
	 *
	 * Also we have to clear buffer_mapped flag of a truncated buffer
	 * because the buffer_head may be attached to the page straddling
	 * i_size (can happen only when blocksize < pagesize) and thus the
	 * buffer_head can be reused when the file is extended again. So we end
	 * up keeping around invalidated buffers attached to transactions'
	 * BJ_Forget list just to stop checkpointing code from cleaning up
	 * the transaction this buffer was modified in.
	 */
	transaction = jh->b_transaction;
	if (transaction == NULL) {
		/* First case: not on any transaction.  If it
		 * has no checkpoint link, then we can zap it:
		 * it's a writeback-mode buffer so we don't care
		 * if it hits disk safely. */
		if (!jh->b_cp_transaction) {
			JBUFFER_TRACE(jh, "not on any transaction: zap");
			goto zap_buffer;
		}

		if (!buffer_dirty(bh)) {
			/* bdflush has written it.  We can drop it now */
			__jbd2_journal_remove_checkpoint(jh);
			goto zap_buffer;
		}

		/* OK, it must be in the journal but still not
		 * written fully to disk: it's metadata or
		 * journaled data... */

		if (journal->j_running_transaction) {
			/* ... and once the current transaction has
			 * committed, the buffer won't be needed any
			 * longer. */
			JBUFFER_TRACE(jh, "checkpointed: add to BJ_Forget");
			may_free = __dispose_buffer(jh,
					journal->j_running_transaction);
			goto zap_buffer;
		} else {
			/* There is no currently-running transaction. So the
			 * orphan record which we wrote for this file must have
			 * passed into commit.  We must attach this buffer to
			 * the committing transaction, if it exists. */
			if (journal->j_committing_transaction) {
				JBUFFER_TRACE(jh, "give to committing trans");
				may_free = __dispose_buffer(jh,
					journal->j_committing_transaction);
				goto zap_buffer;
			} else {
				/* The orphan record's transaction has
				 * committed.  We can cleanse this buffer */
				clear_buffer_jbddirty(bh);
				__jbd2_journal_remove_checkpoint(jh);
				goto zap_buffer;
			}
		}
	} else if (transaction == journal->j_committing_transaction) {
		JBUFFER_TRACE(jh, "on committing transaction");
		/*
		 * The buffer is committing, we simply cannot touch
		 * it. If the page is straddling i_size we have to wait
		 * for commit and try again.
		 */
		if (partial_page) {
			spin_unlock(&journal->j_list_lock);
			spin_unlock(&jh->b_state_lock);
			write_unlock(&journal->j_state_lock);
			jbd2_journal_put_journal_head(jh);
			return -EBUSY;
		}
		/*
		 * OK, buffer won't be reachable after truncate. We just clear
		 * b_modified to not confuse transaction credit accounting, and
		 * set j_next_transaction to the running transaction (if there
		 * is one) and mark buffer as freed so that commit code knows
		 * it should clear dirty bits when it is done with the buffer.
		 */
		set_buffer_freed(bh);
		if (journal->j_running_transaction && buffer_jbddirty(bh))
			jh->b_next_transaction = journal->j_running_transaction;
		jh->b_modified = 0;
		spin_unlock(&journal->j_list_lock);
		spin_unlock(&jh->b_state_lock);
		write_unlock(&journal->j_state_lock);
		jbd2_journal_put_journal_head(jh);
		return 0;
	} else {
		/* Good, the buffer belongs to the running transaction.
		 * We are writing our own transaction's data, not any
		 * previous one's, so it is safe to throw it away
		 * (remember that we expect the filesystem to have set
		 * i_size already for this truncate so recovery will not
		 * expose the disk blocks we are discarding here.) */
		J_ASSERT_JH(jh, transaction == journal->j_running_transaction);
		JBUFFER_TRACE(jh, "on running transaction");
		may_free = __dispose_buffer(jh, transaction);
	}

zap_buffer:
	/*
	 * This is tricky. Although the buffer is truncated, it may be reused
	 * if blocksize < pagesize and it is attached to the page straddling
	 * EOF. Since the buffer might have been added to BJ_Forget list of the
	 * running transaction, journal_get_write_access() won't clear
	 * b_modified and credit accounting gets confused. So clear b_modified
	 * here.
	 */
	jh->b_modified = 0;
	spin_unlock(&journal->j_list_lock);
	spin_unlock(&jh->b_state_lock);
	write_unlock(&journal->j_state_lock);
	jbd2_journal_put_journal_head(jh);
zap_buffer_unlocked:
	clear_buffer_dirty(bh);
	J_ASSERT_BH(bh, !buffer_jbddirty(bh));
	clear_buffer_mapped(bh);
	clear_buffer_req(bh);
	clear_buffer_new(bh);
	clear_buffer_delay(bh);
	clear_buffer_unwritten(bh);
	bh->b_bdev = NULL;
	return may_free;
}

/**
 * void jbd2_journal_invalidatepage()
 * @journal: journal to use for flush...
 * @page:    page to flush
 * @offset:  start of the range to invalidate
 * @length:  length of the range to invalidate
 *
 * Reap page buffers containing data after in the specified range in page.
 * Can return -EBUSY if buffers are part of the committing transaction and
 * the page is straddling i_size. Caller then has to wait for current commit
 * and try again.
 */
int jbd2_journal_invalidatepage(journal_t *journal,
				struct page *page,
				unsigned int offset,
				unsigned int length)
{
	struct buffer_head *head, *bh, *next;
	unsigned int stop = offset + length;
	unsigned int curr_off = 0;
	int partial_page = (offset || length < PAGE_SIZE);
	int may_free = 1;
	int ret = 0;

	if (!PageLocked(page))
		BUG();
	if (!page_has_buffers(page))
		return 0;

	BUG_ON(stop > PAGE_SIZE || stop < length);

	/* We will potentially be playing with lists other than just the
	 * data lists (especially for journaled data mode), so be
	 * cautious in our locking. */

	head = bh = page_buffers(page);
	do {
		unsigned int next_off = curr_off + bh->b_size;
		next = bh->b_this_page;

		if (next_off > stop)
			return 0;

		if (offset <= curr_off) {
			/* This block is wholly outside the truncation point */
			lock_buffer(bh);
			ret = journal_unmap_buffer(journal, bh, partial_page);
			unlock_buffer(bh);
			if (ret < 0)
				return ret;
			may_free &= ret;
		}
		curr_off = next_off;
		bh = next;

	} while (bh != head);

	if (!partial_page) {
		if (may_free && try_to_free_buffers(page))
			J_ASSERT(!page_has_buffers(page));
	}
	return 0;
}

/*
 * File a buffer on the given transaction list.
 */
void __jbd2_journal_file_buffer(struct journal_head *jh,
			transaction_t *transaction, int jlist)
{
	struct journal_head **list = NULL;
	int was_dirty = 0;
	struct buffer_head *bh = jh2bh(jh);

	lockdep_assert_held(&jh->b_state_lock);
	assert_spin_locked(&transaction->t_journal->j_list_lock);

	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
	J_ASSERT_JH(jh, jh->b_transaction == transaction ||
				jh->b_transaction == NULL);

	if (jh->b_transaction && jh->b_jlist == jlist)
		return;

	if (jlist == BJ_Metadata || jlist == BJ_Reserved ||
	    jlist == BJ_Shadow || jlist == BJ_Forget) {
		/*
		 * For metadata buffers, we track dirty bit in buffer_jbddirty
		 * instead of buffer_dirty. We should not see a dirty bit set
		 * here because we clear it in do_get_write_access but e.g.
		 * tune2fs can modify the sb and set the dirty bit at any time
		 * so we try to gracefully handle that.
		 */
		if (buffer_dirty(bh))
			warn_dirty_buffer(bh);
		if (test_clear_buffer_dirty(bh) ||
		    test_clear_buffer_jbddirty(bh))
			was_dirty = 1;
	}

	if (jh->b_transaction)
		__jbd2_journal_temp_unlink_buffer(jh);
	else
		jbd2_journal_grab_journal_head(bh);
	jh->b_transaction = transaction;

	switch (jlist) {
	case BJ_None:
		J_ASSERT_JH(jh, !jh->b_committed_data);
		J_ASSERT_JH(jh, !jh->b_frozen_data);
		return;
	case BJ_Metadata:
		transaction->t_nr_buffers++;
		list = &transaction->t_buffers;
		break;
	case BJ_Forget:
		list = &transaction->t_forget;
		break;
	case BJ_Shadow:
		list = &transaction->t_shadow_list;
		break;
	case BJ_Reserved:
		list = &transaction->t_reserved_list;
		break;
	}

	__blist_add_buffer(list, jh);
	jh->b_jlist = jlist;

	if (was_dirty)
		set_buffer_jbddirty(bh);
}

void jbd2_journal_file_buffer(struct journal_head *jh,
				transaction_t *transaction, int jlist)
{
	spin_lock(&jh->b_state_lock);
	spin_lock(&transaction->t_journal->j_list_lock);
	__jbd2_journal_file_buffer(jh, transaction, jlist);
	spin_unlock(&transaction->t_journal->j_list_lock);
	spin_unlock(&jh->b_state_lock);
}

/*
 * Remove a buffer from its current buffer list in preparation for
 * dropping it from its current transaction entirely.  If the buffer has
 * already started to be used by a subsequent transaction, refile the
 * buffer on that transaction's metadata list.
 *
 * Called under j_list_lock
 * Called under jh->b_state_lock
 *
 * When this function returns true, there's no next transaction to refile to
 * and the caller has to drop jh reference through
 * jbd2_journal_put_journal_head().
 */
bool __jbd2_journal_refile_buffer(struct journal_head *jh)
{
	int was_dirty, jlist;
	struct buffer_head *bh = jh2bh(jh);

	lockdep_assert_held(&jh->b_state_lock);
	if (jh->b_transaction)
		assert_spin_locked(&jh->b_transaction->t_journal->j_list_lock);

	/* If the buffer is now unused, just drop it. */
	if (jh->b_next_transaction == NULL) {
		__jbd2_journal_unfile_buffer(jh);
		return true;
	}

	/*
	 * It has been modified by a later transaction: add it to the new
	 * transaction's metadata list.
	 */

	was_dirty = test_clear_buffer_jbddirty(bh);
	__jbd2_journal_temp_unlink_buffer(jh);

	/*
	 * b_transaction must be set, otherwise the new b_transaction won't
	 * be holding jh reference
	 */
	J_ASSERT_JH(jh, jh->b_transaction != NULL);

	/*
	 * We set b_transaction here because b_next_transaction will inherit
	 * our jh reference and thus __jbd2_journal_file_buffer() must not
	 * take a new one.
	 */
	WRITE_ONCE(jh->b_transaction, jh->b_next_transaction);
	WRITE_ONCE(jh->b_next_transaction, NULL);
	if (buffer_freed(bh))
		jlist = BJ_Forget;
	else if (jh->b_modified)
		jlist = BJ_Metadata;
	else
		jlist = BJ_Reserved;
	__jbd2_journal_file_buffer(jh, jh->b_transaction, jlist);
	J_ASSERT_JH(jh, jh->b_transaction->t_state == T_RUNNING);

	if (was_dirty)
		set_buffer_jbddirty(bh);
	return false;
}

/*
 * __jbd2_journal_refile_buffer() with necessary locking added. We take our
 * bh reference so that we can safely unlock bh.
 *
 * The jh and bh may be freed by this call.
 */
void jbd2_journal_refile_buffer(journal_t *journal, struct journal_head *jh)
{
	bool drop;

	spin_lock(&jh->b_state_lock);
	spin_lock(&journal->j_list_lock);
	drop = __jbd2_journal_refile_buffer(jh);
	spin_unlock(&jh->b_state_lock);
	spin_unlock(&journal->j_list_lock);
	if (drop)
		jbd2_journal_put_journal_head(jh);
}

/*
 * File inode in the inode list of the handle's transaction
 */
static int jbd2_journal_file_inode(handle_t *handle, struct jbd2_inode *jinode,
		unsigned long flags, loff_t start_byte, loff_t end_byte)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal;

	if (is_handle_aborted(handle))
		return -EROFS;
	journal = transaction->t_journal;

	jbd_debug(4, "Adding inode %lu, tid:%d\n", jinode->i_vfs_inode->i_ino,
			transaction->t_tid);

	spin_lock(&journal->j_list_lock);
	jinode->i_flags |= flags;

	if (jinode->i_dirty_end) {
		jinode->i_dirty_start = min(jinode->i_dirty_start, start_byte);
		jinode->i_dirty_end = max(jinode->i_dirty_end, end_byte);
	} else {
		jinode->i_dirty_start = start_byte;
		jinode->i_dirty_end = end_byte;
	}

	/* Is inode already attached where we need it? */
	if (jinode->i_transaction == transaction ||
	    jinode->i_next_transaction == transaction)
		goto done;

	/*
	 * We only ever set this variable to 1 so the test is safe. Since
	 * t_need_data_flush is likely to be set, we do the test to save some
	 * cacheline bouncing
	 */
	if (!transaction->t_need_data_flush)
		transaction->t_need_data_flush = 1;
	/* On some different transaction's list - should be
	 * the committing one */
	if (jinode->i_transaction) {
		J_ASSERT(jinode->i_next_transaction == NULL);
		J_ASSERT(jinode->i_transaction ==
					journal->j_committing_transaction);
		jinode->i_next_transaction = transaction;
		goto done;
	}
	/* Not on any transaction list... */
	J_ASSERT(!jinode->i_next_transaction);
	jinode->i_transaction = transaction;
	list_add(&jinode->i_list, &transaction->t_inode_list);
done:
	spin_unlock(&journal->j_list_lock);

	return 0;
}

int jbd2_journal_inode_ranged_write(handle_t *handle,
		struct jbd2_inode *jinode, loff_t start_byte, loff_t length)
{
	return jbd2_journal_file_inode(handle, jinode,
			JI_WRITE_DATA | JI_WAIT_DATA, start_byte,
			start_byte + length - 1);
}

int jbd2_journal_inode_ranged_wait(handle_t *handle, struct jbd2_inode *jinode,
		loff_t start_byte, loff_t length)
{
	return jbd2_journal_file_inode(handle, jinode, JI_WAIT_DATA,
			start_byte, start_byte + length - 1);
}

/*
 * File truncate and transaction commit interact with each other in a
 * non-trivial way.  If a transaction writing data block A is
 * committing, we cannot discard the data by truncate until we have
 * written them.  Otherwise if we crashed after the transaction with
 * write has committed but before the transaction with truncate has
 * committed, we could see stale data in block A.  This function is a
 * helper to solve this problem.  It starts writeout of the truncated
 * part in case it is in the committing transaction.
 *
 * Filesystem code must call this function when inode is journaled in
 * ordered mode before truncation happens and after the inode has been
 * placed on orphan list with the new inode size. The second condition
 * avoids the race that someone writes new data and we start
 * committing the transaction after this function has been called but
 * before a transaction for truncate is started (and furthermore it
 * allows us to optimize the case where the addition to orphan list
 * happens in the same transaction as write --- we don't have to write
 * any data in such case).
 */
int jbd2_journal_begin_ordered_truncate(journal_t *journal,
					struct jbd2_inode *jinode,
					loff_t new_size)
{
	transaction_t *inode_trans, *commit_trans;
	int ret = 0;

	/* This is a quick check to avoid locking if not necessary */
	if (!jinode->i_transaction)
		goto out;
	/* Locks are here just to force reading of recent values, it is
	 * enough that the transaction was not committing before we started
	 * a transaction adding the inode to orphan list */
	read_lock(&journal->j_state_lock);
	commit_trans = journal->j_committing_transaction;
	read_unlock(&journal->j_state_lock);
	spin_lock(&journal->j_list_lock);
	inode_trans = jinode->i_transaction;
	spin_unlock(&journal->j_list_lock);
	if (inode_trans == commit_trans) {
		ret = filemap_fdatawrite_range(jinode->i_vfs_inode->i_mapping,
			new_size, LLONG_MAX);
		if (ret)
			jbd2_journal_abort(journal, ret);
	}
out:
	return ret;
}