summaryrefslogtreecommitdiffstats
path: root/fs/notify/mark.c
blob: 7abb73b5beba6d8284fb7231379828ba52158a07 (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
/*
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@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, or (at your option)
 *  any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; see the file COPYING.  If not, write to
 *  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * fsnotify inode mark locking/lifetime/and refcnting
 *
 * REFCNT:
 * The group->recnt and mark->refcnt tell how many "things" in the kernel
 * currently are referencing the objects. Both kind of objects typically will
 * live inside the kernel with a refcnt of 2, one for its creation and one for
 * the reference a group and a mark hold to each other.
 * If you are holding the appropriate locks, you can take a reference and the
 * object itself is guaranteed to survive until the reference is dropped.
 *
 * LOCKING:
 * There are 3 locks involved with fsnotify inode marks and they MUST be taken
 * in order as follows:
 *
 * group->mark_mutex
 * mark->lock
 * mark->connector->lock
 *
 * group->mark_mutex protects the marks_list anchored inside a given group and
 * each mark is hooked via the g_list.  It also protects the groups private
 * data (i.e group limits).

 * mark->lock protects the marks attributes like its masks and flags.
 * Furthermore it protects the access to a reference of the group that the mark
 * is assigned to as well as the access to a reference of the inode/vfsmount
 * that is being watched by the mark.
 *
 * mark->connector->lock protects the list of marks anchored inside an
 * inode / vfsmount and each mark is hooked via the i_list.
 *
 * A list of notification marks relating to inode / mnt is contained in
 * fsnotify_mark_connector. That structure is alive as long as there are any
 * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets
 * detached from fsnotify_mark_connector when last reference to the mark is
 * dropped.  Thus having mark reference is enough to protect mark->connector
 * pointer and to make sure fsnotify_mark_connector cannot disappear. Also
 * because we remove mark from g_list before dropping mark reference associated
 * with that, any mark found through g_list is guaranteed to have
 * mark->connector set until we drop group->mark_mutex.
 *
 * LIFETIME:
 * Inode marks survive between when they are added to an inode and when their
 * refcnt==0. Marks are also protected by fsnotify_mark_srcu.
 *
 * The inode mark can be cleared for a number of different reasons including:
 * - The inode is unlinked for the last time.  (fsnotify_inode_remove)
 * - The inode is being evicted from cache. (fsnotify_inode_delete)
 * - The fs the inode is on is unmounted.  (fsnotify_inode_delete/fsnotify_unmount_inodes)
 * - Something explicitly requests that it be removed.  (fsnotify_destroy_mark)
 * - The fsnotify_group associated with the mark is going away and all such marks
 *   need to be cleaned up. (fsnotify_clear_marks_by_group)
 *
 * This has the very interesting property of being able to run concurrently with
 * any (or all) other directions.
 */

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/srcu.h>

#include <linux/atomic.h>

#include <linux/fsnotify_backend.h>
#include "fsnotify.h"

#define FSNOTIFY_REAPER_DELAY	(1)	/* 1 jiffy */

struct srcu_struct fsnotify_mark_srcu;
struct kmem_cache *fsnotify_mark_connector_cachep;

static DEFINE_SPINLOCK(destroy_lock);
static LIST_HEAD(destroy_list);
static struct fsnotify_mark_connector *connector_destroy_list;

static void fsnotify_mark_destroy_workfn(struct work_struct *work);
static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy_workfn);

static void fsnotify_connector_destroy_workfn(struct work_struct *work);
static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn);

void fsnotify_get_mark(struct fsnotify_mark *mark)
{
	WARN_ON_ONCE(!refcount_read(&mark->refcnt));
	refcount_inc(&mark->refcnt);
}

static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
{
	u32 new_mask = 0;
	struct fsnotify_mark *mark;

	assert_spin_locked(&conn->lock);
	hlist_for_each_entry(mark, &conn->list, obj_list) {
		if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)
			new_mask |= mark->mask;
	}
	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
		conn->inode->i_fsnotify_mask = new_mask;
	else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT)
		real_mount(conn->mnt)->mnt_fsnotify_mask = new_mask;
}

/*
 * Calculate mask of events for a list of marks. The caller must make sure
 * connector and connector->inode cannot disappear under us.  Callers achieve
 * this by holding a mark->lock or mark->group->mark_mutex for a mark on this
 * list.
 */
void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
{
	if (!conn)
		return;

	spin_lock(&conn->lock);
	__fsnotify_recalc_mask(conn);
	spin_unlock(&conn->lock);
	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
		__fsnotify_update_child_dentry_flags(conn->inode);
}

/* Free all connectors queued for freeing once SRCU period ends */
static void fsnotify_connector_destroy_workfn(struct work_struct *work)
{
	struct fsnotify_mark_connector *conn, *free;

	spin_lock(&destroy_lock);
	conn = connector_destroy_list;
	connector_destroy_list = NULL;
	spin_unlock(&destroy_lock);

	synchronize_srcu(&fsnotify_mark_srcu);
	while (conn) {
		free = conn;
		conn = conn->destroy_next;
		kmem_cache_free(fsnotify_mark_connector_cachep, free);
	}
}

static struct inode *fsnotify_detach_connector_from_object(
					struct fsnotify_mark_connector *conn)
{
	struct inode *inode = NULL;

	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) {
		inode = conn->inode;
		rcu_assign_pointer(inode->i_fsnotify_marks, NULL);
		inode->i_fsnotify_mask = 0;
		conn->inode = NULL;
		conn->type = FSNOTIFY_OBJ_TYPE_DETACHED;
	} else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) {
		rcu_assign_pointer(real_mount(conn->mnt)->mnt_fsnotify_marks,
				   NULL);
		real_mount(conn->mnt)->mnt_fsnotify_mask = 0;
		conn->mnt = NULL;
		conn->type = FSNOTIFY_OBJ_TYPE_DETACHED;
	}

	return inode;
}

static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark)
{
	struct fsnotify_group *group = mark->group;

	if (WARN_ON_ONCE(!group))
		return;
	group->ops->free_mark(mark);
	fsnotify_put_group(group);
}

void fsnotify_put_mark(struct fsnotify_mark *mark)
{
	struct fsnotify_mark_connector *conn;
	struct inode *inode = NULL;
	bool free_conn = false;

	/* Catch marks that were actually never attached to object */
	if (!mark->connector) {
		if (refcount_dec_and_test(&mark->refcnt))
			fsnotify_final_mark_destroy(mark);
		return;
	}

	/*
	 * We have to be careful so that traversals of obj_list under lock can
	 * safely grab mark reference.
	 */
	if (!refcount_dec_and_lock(&mark->refcnt, &mark->connector->lock))
		return;

	conn = mark->connector;
	hlist_del_init_rcu(&mark->obj_list);
	if (hlist_empty(&conn->list)) {
		inode = fsnotify_detach_connector_from_object(conn);
		free_conn = true;
	} else {
		__fsnotify_recalc_mask(conn);
	}
	mark->connector = NULL;
	spin_unlock(&conn->lock);

	iput(inode);

	if (free_conn) {
		spin_lock(&destroy_lock);
		conn->destroy_next = connector_destroy_list;
		connector_destroy_list = conn;
		spin_unlock(&destroy_lock);
		queue_work(system_unbound_wq, &connector_reaper_work);
	}
	/*
	 * Note that we didn't update flags telling whether inode cares about
	 * what's happening with children. We update these flags from
	 * __fsnotify_parent() lazily when next event happens on one of our
	 * children.
	 */
	spin_lock(&destroy_lock);
	list_add(&mark->g_list, &destroy_list);
	spin_unlock(&destroy_lock);
	queue_delayed_work(system_unbound_wq, &reaper_work,
			   FSNOTIFY_REAPER_DELAY);
}

/*
 * Get mark reference when we found the mark via lockless traversal of object
 * list. Mark can be already removed from the list by now and on its way to be
 * destroyed once SRCU period ends.
 *
 * Also pin the group so it doesn't disappear under us.
 */
static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
{
	if (!mark)
		return true;

	if (refcount_inc_not_zero(&mark->refcnt)) {
		spin_lock(&mark->lock);
		if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
			/* mark is attached, group is still alive then */
			atomic_inc(&mark->group->user_waits);
			spin_unlock(&mark->lock);
			return true;
		}
		spin_unlock(&mark->lock);
		fsnotify_put_mark(mark);
	}
	return false;
}

/*
 * Puts marks and wakes up group destruction if necessary.
 *
 * Pairs with fsnotify_get_mark_safe()
 */
static void fsnotify_put_mark_wake(struct fsnotify_mark *mark)
{
	if (mark) {
		struct fsnotify_group *group = mark->group;

		fsnotify_put_mark(mark);
		/*
		 * We abuse notification_waitq on group shutdown for waiting for
		 * all marks pinned when waiting for userspace.
		 */
		if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
			wake_up(&group->notification_waitq);
	}
}

bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
{
	int type;

	fsnotify_foreach_obj_type(type) {
		/* This can fail if mark is being removed */
		if (!fsnotify_get_mark_safe(iter_info->marks[type]))
			goto fail;
	}

	/*
	 * Now that both marks are pinned by refcount in the inode / vfsmount
	 * lists, we can drop SRCU lock, and safely resume the list iteration
	 * once userspace returns.
	 */
	srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);

	return true;

fail:
	for (type--; type >= 0; type--)
		fsnotify_put_mark_wake(iter_info->marks[type]);
	return false;
}

void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
{
	int type;

	iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
	fsnotify_foreach_obj_type(type)
		fsnotify_put_mark_wake(iter_info->marks[type]);
}

/*
 * Mark mark as detached, remove it from group list. Mark still stays in object
 * list until its last reference is dropped. Note that we rely on mark being
 * removed from group list before corresponding reference to it is dropped. In
 * particular we rely on mark->connector being valid while we hold
 * group->mark_mutex if we found the mark through g_list.
 *
 * Must be called with group->mark_mutex held. The caller must either hold
 * reference to the mark or be protected by fsnotify_mark_srcu.
 */
void fsnotify_detach_mark(struct fsnotify_mark *mark)
{
	struct fsnotify_group *group = mark->group;

	WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
	WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
		     refcount_read(&mark->refcnt) < 1 +
			!!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));

	spin_lock(&mark->lock);
	/* something else already called this function on this mark */
	if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
		spin_unlock(&mark->lock);
		return;
	}
	mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
	list_del_init(&mark->g_list);
	spin_unlock(&mark->lock);

	atomic_dec(&group->num_marks);

	/* Drop mark reference acquired in fsnotify_add_mark_locked() */
	fsnotify_put_mark(mark);
}

/*
 * Free fsnotify mark. The mark is actually only marked as being freed.  The
 * freeing is actually happening only once last reference to the mark is
 * dropped from a workqueue which first waits for srcu period end.
 *
 * Caller must have a reference to the mark or be protected by
 * fsnotify_mark_srcu.
 */
void fsnotify_free_mark(struct fsnotify_mark *mark)
{
	struct fsnotify_group *group = mark->group;

	spin_lock(&mark->lock);
	/* something else already called this function on this mark */
	if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
		spin_unlock(&mark->lock);
		return;
	}
	mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
	spin_unlock(&mark->lock);

	/*
	 * Some groups like to know that marks are being freed.  This is a
	 * callback to the group function to let it know that this mark
	 * is being freed.
	 */
	if (group->ops->freeing_mark)
		group->ops->freeing_mark(mark, group);
}

void fsnotify_destroy_mark(struct fsnotify_mark *mark,
			   struct fsnotify_group *group)
{
	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
	fsnotify_detach_mark(mark);
	mutex_unlock(&group->mark_mutex);
	fsnotify_free_mark(mark);
}

/*
 * Sorting function for lists of fsnotify marks.
 *
 * Fanotify supports different notification classes (reflected as priority of
 * notification group). Events shall be passed to notification groups in
 * decreasing priority order. To achieve this marks in notification lists for
 * inodes and vfsmounts are sorted so that priorities of corresponding groups
 * are descending.
 *
 * Furthermore correct handling of the ignore mask requires processing inode
 * and vfsmount marks of each group together. Using the group address as
 * further sort criterion provides a unique sorting order and thus we can
 * merge inode and vfsmount lists of marks in linear time and find groups
 * present in both lists.
 *
 * A return value of 1 signifies that b has priority over a.
 * A return value of 0 signifies that the two marks have to be handled together.
 * A return value of -1 signifies that a has priority over b.
 */
int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
{
	if (a == b)
		return 0;
	if (!a)
		return 1;
	if (!b)
		return -1;
	if (a->priority < b->priority)
		return 1;
	if (a->priority > b->priority)
		return -1;
	if (a < b)
		return 1;
	return -1;
}

static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
					       unsigned int type)
{
	struct inode *inode = NULL;
	struct fsnotify_mark_connector *conn;

	conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);
	if (!conn)
		return -ENOMEM;
	spin_lock_init(&conn->lock);
	INIT_HLIST_HEAD(&conn->list);
	conn->type = type;
	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
		inode = conn->inode = igrab(fsnotify_obj_inode(connp));
	else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT)
		conn->mnt = &fsnotify_obj_mount(connp)->mnt;
	/*
	 * cmpxchg() provides the barrier so that readers of *connp can see
	 * only initialized structure
	 */
	if (cmpxchg(connp, NULL, conn)) {
		/* Someone else created list structure for us */
		if (inode)
			iput(inode);
		kmem_cache_free(fsnotify_mark_connector_cachep, conn);
	}

	return 0;
}

/*
 * Get mark connector, make sure it is alive and return with its lock held.
 * This is for users that get connector pointer from inode or mount. Users that
 * hold reference to a mark on the list may directly lock connector->lock as
 * they are sure list cannot go away under them.
 */
static struct fsnotify_mark_connector *fsnotify_grab_connector(
						fsnotify_connp_t *connp)
{
	struct fsnotify_mark_connector *conn;
	int idx;

	idx = srcu_read_lock(&fsnotify_mark_srcu);
	conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
	if (!conn)
		goto out;
	spin_lock(&conn->lock);
	if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) {
		spin_unlock(&conn->lock);
		srcu_read_unlock(&fsnotify_mark_srcu, idx);
		return NULL;
	}
out:
	srcu_read_unlock(&fsnotify_mark_srcu, idx);
	return conn;
}

/*
 * Add mark into proper place in given list of marks. These marks may be used
 * for the fsnotify backend to determine which event types should be delivered
 * to which group and for which inodes. These marks are ordered according to
 * priority, highest number first, and then by the group's location in memory.
 */
static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
				  fsnotify_connp_t *connp, unsigned int type,
				  int allow_dups)
{
	struct fsnotify_mark *lmark, *last = NULL;
	struct fsnotify_mark_connector *conn;
	int cmp;
	int err = 0;

	if (WARN_ON(!fsnotify_valid_obj_type(type)))
		return -EINVAL;
restart:
	spin_lock(&mark->lock);
	conn = fsnotify_grab_connector(connp);
	if (!conn) {
		spin_unlock(&mark->lock);
		err = fsnotify_attach_connector_to_object(connp, type);
		if (err)
			return err;
		goto restart;
	}

	/* is mark the first mark? */
	if (hlist_empty(&conn->list)) {
		hlist_add_head_rcu(&mark->obj_list, &conn->list);
		goto added;
	}

	/* should mark be in the middle of the current list? */
	hlist_for_each_entry(lmark, &conn->list, obj_list) {
		last = lmark;

		if ((lmark->group == mark->group) &&
		    (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) &&
		    !allow_dups) {
			err = -EEXIST;
			goto out_err;
		}

		cmp = fsnotify_compare_groups(lmark->group, mark->group);
		if (cmp >= 0) {
			hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
			goto added;
		}
	}

	BUG_ON(last == NULL);
	/* mark should be the last entry.  last is the current last entry */
	hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
added:
	mark->connector = conn;
out_err:
	spin_unlock(&conn->lock);
	spin_unlock(&mark->lock);
	return err;
}

/*
 * Attach an initialized mark to a given group and fs object.
 * These marks may be used for the fsnotify backend to determine which
 * event types should be delivered to which group.
 */
int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
			     fsnotify_connp_t *connp, unsigned int type,
			     int allow_dups)
{
	struct fsnotify_group *group = mark->group;
	int ret = 0;

	BUG_ON(!mutex_is_locked(&group->mark_mutex));

	/*
	 * LOCKING ORDER!!!!
	 * group->mark_mutex
	 * mark->lock
	 * mark->connector->lock
	 */
	spin_lock(&mark->lock);
	mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;

	list_add(&mark->g_list, &group->marks_list);
	atomic_inc(&group->num_marks);
	fsnotify_get_mark(mark); /* for g_list */
	spin_unlock(&mark->lock);

	ret = fsnotify_add_mark_list(mark, connp, type, allow_dups);
	if (ret)
		goto err;

	if (mark->mask)
		fsnotify_recalc_mask(mark->connector);

	return ret;
err:
	spin_lock(&mark->lock);
	mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE |
			 FSNOTIFY_MARK_FLAG_ATTACHED);
	list_del_init(&mark->g_list);
	spin_unlock(&mark->lock);
	atomic_dec(&group->num_marks);

	fsnotify_put_mark(mark);
	return ret;
}

int fsnotify_add_mark(struct fsnotify_mark *mark, fsnotify_connp_t *connp,
		      unsigned int type, int allow_dups)
{
	int ret;
	struct fsnotify_group *group = mark->group;

	mutex_lock(&group->mark_mutex);
	ret = fsnotify_add_mark_locked(mark, connp, type, allow_dups);
	mutex_unlock(&group->mark_mutex);
	return ret;
}

/*
 * Given a list of marks, find the mark associated with given group. If found
 * take a reference to that mark and return it, else return NULL.
 */
struct fsnotify_mark *fsnotify_find_mark(fsnotify_connp_t *connp,
					 struct fsnotify_group *group)
{
	struct fsnotify_mark_connector *conn;
	struct fsnotify_mark *mark;

	conn = fsnotify_grab_connector(connp);
	if (!conn)
		return NULL;

	hlist_for_each_entry(mark, &conn->list, obj_list) {
		if (mark->group == group &&
		    (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
			fsnotify_get_mark(mark);
			spin_unlock(&conn->lock);
			return mark;
		}
	}
	spin_unlock(&conn->lock);
	return NULL;
}

/* Clear any marks in a group with given type mask */
void fsnotify_clear_marks_by_group(struct fsnotify_group *group,
				   unsigned int type_mask)
{
	struct fsnotify_mark *lmark, *mark;
	LIST_HEAD(to_free);
	struct list_head *head = &to_free;

	/* Skip selection step if we want to clear all marks. */
	if (type_mask == FSNOTIFY_OBJ_ALL_TYPES_MASK) {
		head = &group->marks_list;
		goto clear;
	}
	/*
	 * We have to be really careful here. Anytime we drop mark_mutex, e.g.
	 * fsnotify_clear_marks_by_inode() can come and free marks. Even in our
	 * to_free list so we have to use mark_mutex even when accessing that
	 * list. And freeing mark requires us to drop mark_mutex. So we can
	 * reliably free only the first mark in the list. That's why we first
	 * move marks to free to to_free list in one go and then free marks in
	 * to_free list one by one.
	 */
	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
	list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
		if ((1U << mark->connector->type) & type_mask)
			list_move(&mark->g_list, &to_free);
	}
	mutex_unlock(&group->mark_mutex);

clear:
	while (1) {
		mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
		if (list_empty(head)) {
			mutex_unlock(&group->mark_mutex);
			break;
		}
		mark = list_first_entry(head, struct fsnotify_mark, g_list);
		fsnotify_get_mark(mark);
		fsnotify_detach_mark(mark);
		mutex_unlock(&group->mark_mutex);
		fsnotify_free_mark(mark);
		fsnotify_put_mark(mark);
	}
}

/* Destroy all marks attached to an object via connector */
void fsnotify_destroy_marks(fsnotify_connp_t *connp)
{
	struct fsnotify_mark_connector *conn;
	struct fsnotify_mark *mark, *old_mark = NULL;
	struct inode *inode;

	conn = fsnotify_grab_connector(connp);
	if (!conn)
		return;
	/*
	 * We have to be careful since we can race with e.g.
	 * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the
	 * list can get modified. However we are holding mark reference and
	 * thus our mark cannot be removed from obj_list so we can continue
	 * iteration after regaining conn->lock.
	 */
	hlist_for_each_entry(mark, &conn->list, obj_list) {
		fsnotify_get_mark(mark);
		spin_unlock(&conn->lock);
		if (old_mark)
			fsnotify_put_mark(old_mark);
		old_mark = mark;
		fsnotify_destroy_mark(mark, mark->group);
		spin_lock(&conn->lock);
	}
	/*
	 * Detach list from object now so that we don't pin inode until all
	 * mark references get dropped. It would lead to strange results such
	 * as delaying inode deletion or blocking unmount.
	 */
	inode = fsnotify_detach_connector_from_object(conn);
	spin_unlock(&conn->lock);
	if (old_mark)
		fsnotify_put_mark(old_mark);
	iput(inode);
}

/*
 * Nothing fancy, just initialize lists and locks and counters.
 */
void fsnotify_init_mark(struct fsnotify_mark *mark,
			struct fsnotify_group *group)
{
	memset(mark, 0, sizeof(*mark));
	spin_lock_init(&mark->lock);
	refcount_set(&mark->refcnt, 1);
	fsnotify_get_group(group);
	mark->group = group;
}

/*
 * Destroy all marks in destroy_list, waits for SRCU period to finish before
 * actually freeing marks.
 */
static void fsnotify_mark_destroy_workfn(struct work_struct *work)
{
	struct fsnotify_mark *mark, *next;
	struct list_head private_destroy_list;

	spin_lock(&destroy_lock);
	/* exchange the list head */
	list_replace_init(&destroy_list, &private_destroy_list);
	spin_unlock(&destroy_lock);

	synchronize_srcu(&fsnotify_mark_srcu);

	list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
		list_del_init(&mark->g_list);
		fsnotify_final_mark_destroy(mark);
	}
}

/* Wait for all marks queued for destruction to be actually destroyed */
void fsnotify_wait_marks_destroyed(void)
{
	flush_delayed_work(&reaper_work);
}