summaryrefslogtreecommitdiff
path: root/fs/afs/cell.c
blob: 1858c91169e4fc213e77b548628386041790b0c0 (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
/* AFS cell and server record management
 *
 * Copyright (C) 2002, 2017 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/slab.h>
#include <linux/key.h>
#include <linux/ctype.h>
#include <linux/dns_resolver.h>
#include <linux/sched.h>
#include <linux/inet.h>
#include <keys/rxrpc-type.h>
#include "internal.h"

unsigned __read_mostly afs_cell_gc_delay = 10;

static void afs_manage_cell(struct work_struct *);

static void afs_dec_cells_outstanding(struct afs_net *net)
{
	if (atomic_dec_and_test(&net->cells_outstanding))
		wake_up_atomic_t(&net->cells_outstanding);
}

/*
 * Set the cell timer to fire after a given delay, assuming it's not already
 * set for an earlier time.
 */
static void afs_set_cell_timer(struct afs_net *net, time64_t delay)
{
	if (net->live) {
		atomic_inc(&net->cells_outstanding);
		if (timer_reduce(&net->cells_timer, jiffies + delay * HZ))
			afs_dec_cells_outstanding(net);
	}
}

/*
 * Look up and get an activation reference on a cell record under RCU
 * conditions.  The caller must hold the RCU read lock.
 */
struct afs_cell *afs_lookup_cell_rcu(struct afs_net *net,
				     const char *name, unsigned int namesz)
{
	struct afs_cell *cell = NULL;
	struct rb_node *p;
	int n, seq = 0, ret = 0;

	_enter("%*.*s", namesz, namesz, name);

	if (name && namesz == 0)
		return ERR_PTR(-EINVAL);
	if (namesz > AFS_MAXCELLNAME)
		return ERR_PTR(-ENAMETOOLONG);

	do {
		/* Unfortunately, rbtree walking doesn't give reliable results
		 * under just the RCU read lock, so we have to check for
		 * changes.
		 */
		if (cell)
			afs_put_cell(net, cell);
		cell = NULL;
		ret = -ENOENT;

		read_seqbegin_or_lock(&net->cells_lock, &seq);

		if (!name) {
			cell = rcu_dereference_raw(net->ws_cell);
			if (cell) {
				afs_get_cell(cell);
				continue;
			}
			ret = -EDESTADDRREQ;
			continue;
		}

		p = rcu_dereference_raw(net->cells.rb_node);
		while (p) {
			cell = rb_entry(p, struct afs_cell, net_node);

			n = strncasecmp(cell->name, name,
					min_t(size_t, cell->name_len, namesz));
			if (n == 0)
				n = cell->name_len - namesz;
			if (n < 0) {
				p = rcu_dereference_raw(p->rb_left);
			} else if (n > 0) {
				p = rcu_dereference_raw(p->rb_right);
			} else {
				if (atomic_inc_not_zero(&cell->usage)) {
					ret = 0;
					break;
				}
				/* We want to repeat the search, this time with
				 * the lock properly locked.
				 */
			}
			cell = NULL;
		}

	} while (need_seqretry(&net->cells_lock, seq));

	done_seqretry(&net->cells_lock, seq);

	return ret == 0 ? cell : ERR_PTR(ret);
}

/*
 * Set up a cell record and fill in its name, VL server address list and
 * allocate an anonymous key
 */
static struct afs_cell *afs_alloc_cell(struct afs_net *net,
				       const char *name, unsigned int namelen,
				       const char *vllist)
{
	struct afs_cell *cell;
	int i, ret;

	ASSERT(name);
	if (namelen == 0)
		return ERR_PTR(-EINVAL);
	if (namelen > AFS_MAXCELLNAME) {
		_leave(" = -ENAMETOOLONG");
		return ERR_PTR(-ENAMETOOLONG);
	}

	_enter("%*.*s,%s", namelen, namelen, name, vllist);

	cell = kzalloc(sizeof(struct afs_cell), GFP_KERNEL);
	if (!cell) {
		_leave(" = -ENOMEM");
		return ERR_PTR(-ENOMEM);
	}

	cell->net = net;
	cell->name_len = namelen;
	for (i = 0; i < namelen; i++)
		cell->name[i] = tolower(name[i]);

	atomic_set(&cell->usage, 2);
	INIT_WORK(&cell->manager, afs_manage_cell);
	cell->flags = ((1 << AFS_CELL_FL_NOT_READY) |
		       (1 << AFS_CELL_FL_NO_LOOKUP_YET));
	INIT_LIST_HEAD(&cell->proc_volumes);
	rwlock_init(&cell->proc_lock);
	rwlock_init(&cell->vl_addrs_lock);

	/* Fill in the VL server list if we were given a list of addresses to
	 * use.
	 */
	if (vllist) {
		struct afs_addr_list *alist;

		alist = afs_parse_text_addrs(vllist, strlen(vllist), ':',
					     VL_SERVICE, AFS_VL_PORT);
		if (IS_ERR(alist)) {
			ret = PTR_ERR(alist);
			goto parse_failed;
		}

		rcu_assign_pointer(cell->vl_addrs, alist);
		cell->dns_expiry = TIME64_MAX;
	}

	_leave(" = %p", cell);
	return cell;

parse_failed:
	if (ret == -EINVAL)
		printk(KERN_ERR "kAFS: bad VL server IP address\n");
	kfree(cell);
	_leave(" = %d", ret);
	return ERR_PTR(ret);
}

/*
 * afs_lookup_cell - Look up or create a cell record.
 * @net:	The network namespace
 * @name:	The name of the cell.
 * @namesz:	The strlen of the cell name.
 * @vllist:	A colon/comma separated list of numeric IP addresses or NULL.
 * @excl:	T if an error should be given if the cell name already exists.
 *
 * Look up a cell record by name and query the DNS for VL server addresses if
 * needed.  Note that that actual DNS query is punted off to the manager thread
 * so that this function can return immediately if interrupted whilst allowing
 * cell records to be shared even if not yet fully constructed.
 */
struct afs_cell *afs_lookup_cell(struct afs_net *net,
				 const char *name, unsigned int namesz,
				 const char *vllist, bool excl)
{
	struct afs_cell *cell, *candidate, *cursor;
	struct rb_node *parent, **pp;
	int ret, n;

	_enter("%s,%s", name, vllist);

	if (!excl) {
		rcu_read_lock();
		cell = afs_lookup_cell_rcu(net, name, namesz);
		rcu_read_unlock();
		if (!IS_ERR(cell)) {
			if (excl) {
				afs_put_cell(net, cell);
				return ERR_PTR(-EEXIST);
			}
			goto wait_for_cell;
		}
	}

	/* Assume we're probably going to create a cell and preallocate and
	 * mostly set up a candidate record.  We can then use this to stash the
	 * name, the net namespace and VL server addresses.
	 *
	 * We also want to do this before we hold any locks as it may involve
	 * upcalling to userspace to make DNS queries.
	 */
	candidate = afs_alloc_cell(net, name, namesz, vllist);
	if (IS_ERR(candidate)) {
		_leave(" = %ld", PTR_ERR(candidate));
		return candidate;
	}

	/* Find the insertion point and check to see if someone else added a
	 * cell whilst we were allocating.
	 */
	write_seqlock(&net->cells_lock);

	pp = &net->cells.rb_node;
	parent = NULL;
	while (*pp) {
		parent = *pp;
		cursor = rb_entry(parent, struct afs_cell, net_node);

		n = strncasecmp(cursor->name, name,
				min_t(size_t, cursor->name_len, namesz));
		if (n == 0)
			n = cursor->name_len - namesz;
		if (n < 0)
			pp = &(*pp)->rb_left;
		else if (n > 0)
			pp = &(*pp)->rb_right;
		else
			goto cell_already_exists;
	}

	cell = candidate;
	candidate = NULL;
	rb_link_node_rcu(&cell->net_node, parent, pp);
	rb_insert_color(&cell->net_node, &net->cells);
	atomic_inc(&net->cells_outstanding);
	write_sequnlock(&net->cells_lock);

	queue_work(afs_wq, &cell->manager);

wait_for_cell:
	_debug("wait_for_cell");
	ret = wait_on_bit(&cell->flags, AFS_CELL_FL_NOT_READY, TASK_INTERRUPTIBLE);
	smp_rmb();

	switch (READ_ONCE(cell->state)) {
	case AFS_CELL_FAILED:
		ret = cell->error;
		goto error;
	default:
		_debug("weird %u %d", cell->state, cell->error);
		goto error;
	case AFS_CELL_ACTIVE:
		break;
	}

	_leave(" = %p [cell]", cell);
	return cell;

cell_already_exists:
	_debug("cell exists");
	cell = cursor;
	if (excl) {
		ret = -EEXIST;
	} else {
		afs_get_cell(cursor);
		ret = 0;
	}
	write_sequnlock(&net->cells_lock);
	kfree(candidate);
	if (ret == 0)
		goto wait_for_cell;
	goto error_noput;
error:
	afs_put_cell(net, cell);
error_noput:
	_leave(" = %d [error]", ret);
	return ERR_PTR(ret);
}

/*
 * set the root cell information
 * - can be called with a module parameter string
 * - can be called from a write to /proc/fs/afs/rootcell
 */
int afs_cell_init(struct afs_net *net, const char *rootcell)
{
	struct afs_cell *old_root, *new_root;
	const char *cp, *vllist;
	size_t len;

	_enter("");

	if (!rootcell) {
		/* module is loaded with no parameters, or built statically.
		 * - in the future we might initialize cell DB here.
		 */
		_leave(" = 0 [no root]");
		return 0;
	}

	cp = strchr(rootcell, ':');
	if (!cp) {
		_debug("kAFS: no VL server IP addresses specified");
		vllist = NULL;
		len = strlen(rootcell);
	} else {
		vllist = cp + 1;
		len = cp - rootcell;
	}

	/* allocate a cell record for the root cell */
	new_root = afs_lookup_cell(net, rootcell, len, vllist, false);
	if (IS_ERR(new_root)) {
		_leave(" = %ld", PTR_ERR(new_root));
		return PTR_ERR(new_root);
	}

	set_bit(AFS_CELL_FL_NO_GC, &new_root->flags);
	afs_get_cell(new_root);

	/* install the new cell */
	write_seqlock(&net->cells_lock);
	old_root = net->ws_cell;
	net->ws_cell = new_root;
	write_sequnlock(&net->cells_lock);

	afs_put_cell(net, old_root);
	_leave(" = 0");
	return 0;
}

/*
 * Update a cell's VL server address list from the DNS.
 */
static void afs_update_cell(struct afs_cell *cell)
{
	struct afs_addr_list *alist, *old;
	time64_t now, expiry;

	_enter("%s", cell->name);

	alist = afs_dns_query(cell, &expiry);
	if (IS_ERR(alist)) {
		switch (PTR_ERR(alist)) {
		case -ENODATA:
			/* The DNS said that the cell does not exist */
			set_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
			clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
			cell->dns_expiry = ktime_get_real_seconds() + 61;
			break;

		case -EAGAIN:
		case -ECONNREFUSED:
		default:
			set_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
			cell->dns_expiry = ktime_get_real_seconds() + 10;
			break;
		}

		cell->error = -EDESTADDRREQ;
	} else {
		clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
		clear_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);

		/* Exclusion on changing vl_addrs is achieved by a
		 * non-reentrant work item.
		 */
		old = rcu_dereference_protected(cell->vl_addrs, true);
		rcu_assign_pointer(cell->vl_addrs, alist);
		cell->dns_expiry = expiry;

		if (old)
			afs_put_addrlist(old);
	}

	if (test_and_clear_bit(AFS_CELL_FL_NO_LOOKUP_YET, &cell->flags))
		wake_up_bit(&cell->flags, AFS_CELL_FL_NO_LOOKUP_YET);

	now = ktime_get_real_seconds();
	afs_set_cell_timer(cell->net, cell->dns_expiry - now);
	_leave("");
}

/*
 * Destroy a cell record
 */
static void afs_cell_destroy(struct rcu_head *rcu)
{
	struct afs_cell *cell = container_of(rcu, struct afs_cell, rcu);

	_enter("%p{%s}", cell, cell->name);

	ASSERTCMP(atomic_read(&cell->usage), ==, 0);

	afs_put_addrlist(cell->vl_addrs);
	key_put(cell->anonymous_key);
	kfree(cell);

	_leave(" [destroyed]");
}

/*
 * Queue the cell manager.
 */
static void afs_queue_cell_manager(struct afs_net *net)
{
	int outstanding = atomic_inc_return(&net->cells_outstanding);

	_enter("%d", outstanding);

	if (!queue_work(afs_wq, &net->cells_manager))
		afs_dec_cells_outstanding(net);
}

/*
 * Cell management timer.  We have an increment on cells_outstanding that we
 * need to pass along to the work item.
 */
void afs_cells_timer(struct timer_list *timer)
{
	struct afs_net *net = container_of(timer, struct afs_net, cells_timer);

	_enter("");
	if (!queue_work(afs_wq, &net->cells_manager))
		afs_dec_cells_outstanding(net);
}

/*
 * Get a reference on a cell record.
 */
struct afs_cell *afs_get_cell(struct afs_cell *cell)
{
	atomic_inc(&cell->usage);
	return cell;
}

/*
 * Drop a reference on a cell record.
 */
void afs_put_cell(struct afs_net *net, struct afs_cell *cell)
{
	time64_t now, expire_delay;

	if (!cell)
		return;

	_enter("%s", cell->name);

	now = ktime_get_real_seconds();
	cell->last_inactive = now;
	expire_delay = 0;
	if (!test_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags) &&
	    !test_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags))
		expire_delay = afs_cell_gc_delay;

	if (atomic_dec_return(&cell->usage) > 1)
		return;

	/* 'cell' may now be garbage collected. */
	afs_set_cell_timer(net, expire_delay);
}

/*
 * Allocate a key to use as a placeholder for anonymous user security.
 */
static int afs_alloc_anon_key(struct afs_cell *cell)
{
	struct key *key;
	char keyname[4 + AFS_MAXCELLNAME + 1], *cp, *dp;

	/* Create a key to represent an anonymous user. */
	memcpy(keyname, "afs@", 4);
	dp = keyname + 4;
	cp = cell->name;
	do {
		*dp++ = tolower(*cp);
	} while (*cp++);

	key = rxrpc_get_null_key(keyname);
	if (IS_ERR(key))
		return PTR_ERR(key);

	cell->anonymous_key = key;

	_debug("anon key %p{%x}",
	       cell->anonymous_key, key_serial(cell->anonymous_key));
	return 0;
}

/*
 * Activate a cell.
 */
static int afs_activate_cell(struct afs_net *net, struct afs_cell *cell)
{
	int ret;

	if (!cell->anonymous_key) {
		ret = afs_alloc_anon_key(cell);
		if (ret < 0)
			return ret;
	}

#ifdef CONFIG_AFS_FSCACHE
	cell->cache = fscache_acquire_cookie(afs_cache_netfs.primary_index,
					     &afs_cell_cache_index_def,
					     cell, true);
#endif
	ret = afs_proc_cell_setup(net, cell);
	if (ret < 0)
		return ret;
	spin_lock(&net->proc_cells_lock);
	list_add_tail(&cell->proc_link, &net->proc_cells);
	spin_unlock(&net->proc_cells_lock);
	return 0;
}

/*
 * Deactivate a cell.
 */
static void afs_deactivate_cell(struct afs_net *net, struct afs_cell *cell)
{
	_enter("%s", cell->name);

	afs_proc_cell_remove(net, cell);

	spin_lock(&net->proc_cells_lock);
	list_del_init(&cell->proc_link);
	spin_unlock(&net->proc_cells_lock);

#ifdef CONFIG_AFS_FSCACHE
	fscache_relinquish_cookie(cell->cache, 0);
	cell->cache = NULL;
#endif

	_leave("");
}

/*
 * Manage a cell record, initialising and destroying it, maintaining its DNS
 * records.
 */
static void afs_manage_cell(struct work_struct *work)
{
	struct afs_cell *cell = container_of(work, struct afs_cell, manager);
	struct afs_net *net = cell->net;
	bool deleted;
	int ret, usage;

	_enter("%s", cell->name);

again:
	_debug("state %u", cell->state);
	switch (cell->state) {
	case AFS_CELL_INACTIVE:
	case AFS_CELL_FAILED:
		write_seqlock(&net->cells_lock);
		usage = 1;
		deleted = atomic_try_cmpxchg_relaxed(&cell->usage, &usage, 0);
		if (deleted)
			rb_erase(&cell->net_node, &net->cells);
		write_sequnlock(&net->cells_lock);
		if (deleted)
			goto final_destruction;
		if (cell->state == AFS_CELL_FAILED)
			goto done;
		cell->state = AFS_CELL_UNSET;
		goto again;

	case AFS_CELL_UNSET:
		cell->state = AFS_CELL_ACTIVATING;
		goto again;

	case AFS_CELL_ACTIVATING:
		ret = afs_activate_cell(net, cell);
		if (ret < 0)
			goto activation_failed;

		cell->state = AFS_CELL_ACTIVE;
		smp_wmb();
		clear_bit(AFS_CELL_FL_NOT_READY, &cell->flags);
		wake_up_bit(&cell->flags, AFS_CELL_FL_NOT_READY);
		goto again;

	case AFS_CELL_ACTIVE:
		if (atomic_read(&cell->usage) > 1) {
			time64_t now = ktime_get_real_seconds();
			if (cell->dns_expiry <= now && net->live)
				afs_update_cell(cell);
			goto done;
		}
		cell->state = AFS_CELL_DEACTIVATING;
		goto again;

	case AFS_CELL_DEACTIVATING:
		set_bit(AFS_CELL_FL_NOT_READY, &cell->flags);
		if (atomic_read(&cell->usage) > 1)
			goto reverse_deactivation;
		afs_deactivate_cell(net, cell);
		cell->state = AFS_CELL_INACTIVE;
		goto again;

	default:
		break;
	}
	_debug("bad state %u", cell->state);
	BUG(); /* Unhandled state */

activation_failed:
	cell->error = ret;
	afs_deactivate_cell(net, cell);

	cell->state = AFS_CELL_FAILED;
	smp_wmb();
	if (test_and_clear_bit(AFS_CELL_FL_NOT_READY, &cell->flags))
		wake_up_bit(&cell->flags, AFS_CELL_FL_NOT_READY);
	goto again;

reverse_deactivation:
	cell->state = AFS_CELL_ACTIVE;
	smp_wmb();
	clear_bit(AFS_CELL_FL_NOT_READY, &cell->flags);
	wake_up_bit(&cell->flags, AFS_CELL_FL_NOT_READY);
	_leave(" [deact->act]");
	return;

done:
	_leave(" [done %u]", cell->state);
	return;

final_destruction:
	call_rcu(&cell->rcu, afs_cell_destroy);
	afs_dec_cells_outstanding(net);
	_leave(" [destruct %d]", atomic_read(&net->cells_outstanding));
}

/*
 * Manage the records of cells known to a network namespace.  This includes
 * updating the DNS records and garbage collecting unused cells that were
 * automatically added.
 *
 * Note that constructed cell records may only be removed from net->cells by
 * this work item, so it is safe for this work item to stash a cursor pointing
 * into the tree and then return to caller (provided it skips cells that are
 * still under construction).
 *
 * Note also that we were given an increment on net->cells_outstanding by
 * whoever queued us that we need to deal with before returning.
 */
void afs_manage_cells(struct work_struct *work)
{
	struct afs_net *net = container_of(work, struct afs_net, cells_manager);
	struct rb_node *cursor;
	time64_t now = ktime_get_real_seconds(), next_manage = TIME64_MAX;
	bool purging = !net->live;

	_enter("");

	/* Trawl the cell database looking for cells that have expired from
	 * lack of use and cells whose DNS results have expired and dispatch
	 * their managers.
	 */
	read_seqlock_excl(&net->cells_lock);

	for (cursor = rb_first(&net->cells); cursor; cursor = rb_next(cursor)) {
		struct afs_cell *cell =
			rb_entry(cursor, struct afs_cell, net_node);
		unsigned usage;
		bool sched_cell = false;

		usage = atomic_read(&cell->usage);
		_debug("manage %s %u", cell->name, usage);

		ASSERTCMP(usage, >=, 1);

		if (purging) {
			if (test_and_clear_bit(AFS_CELL_FL_NO_GC, &cell->flags))
				usage = atomic_dec_return(&cell->usage);
			ASSERTCMP(usage, ==, 1);
		}

		if (usage == 1) {
			time64_t expire_at = cell->last_inactive;

			if (!test_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags) &&
			    !test_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags))
				expire_at += afs_cell_gc_delay;
			if (purging || expire_at <= now)
				sched_cell = true;
			else if (expire_at < next_manage)
				next_manage = expire_at;
		}

		if (!purging) {
			if (cell->dns_expiry <= now)
				sched_cell = true;
			else if (cell->dns_expiry <= next_manage)
				next_manage = cell->dns_expiry;
		}

		if (sched_cell)
			queue_work(afs_wq, &cell->manager);
	}

	read_sequnlock_excl(&net->cells_lock);

	/* Update the timer on the way out.  We have to pass an increment on
	 * cells_outstanding in the namespace that we are in to the timer or
	 * the work scheduler.
	 */
	if (!purging && next_manage < TIME64_MAX) {
		now = ktime_get_real_seconds();

		if (next_manage - now <= 0) {
			if (queue_work(afs_wq, &net->cells_manager))
				atomic_inc(&net->cells_outstanding);
		} else {
			afs_set_cell_timer(net, next_manage - now);
		}
	}

	afs_dec_cells_outstanding(net);
	_leave(" [%d]", atomic_read(&net->cells_outstanding));
}

/*
 * Purge in-memory cell database.
 */
void afs_cell_purge(struct afs_net *net)
{
	struct afs_cell *ws;

	_enter("");

	write_seqlock(&net->cells_lock);
	ws = net->ws_cell;
	net->ws_cell = NULL;
	write_sequnlock(&net->cells_lock);
	afs_put_cell(net, ws);

	_debug("del timer");
	if (del_timer_sync(&net->cells_timer))
		atomic_dec(&net->cells_outstanding);

	_debug("kick mgr");
	afs_queue_cell_manager(net);

	_debug("wait");
	wait_on_atomic_t(&net->cells_outstanding, atomic_t_wait,
			 TASK_UNINTERRUPTIBLE);
	_leave("");
}