1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  4 */
  5
  6/*
  7 * fsnotify inode mark locking/lifetime/and refcnting
  8 *
  9 * REFCNT:
 10 * The group->recnt and mark->refcnt tell how many "things" in the kernel
 11 * currently are referencing the objects. Both kind of objects typically will
 12 * live inside the kernel with a refcnt of 2, one for its creation and one for
 13 * the reference a group and a mark hold to each other.
 14 * If you are holding the appropriate locks, you can take a reference and the
 15 * object itself is guaranteed to survive until the reference is dropped.
 16 *
 17 * LOCKING:
 18 * There are 3 locks involved with fsnotify inode marks and they MUST be taken
 19 * in order as follows:
 20 *
 21 * group->mark_mutex
 22 * mark->lock
 23 * mark->connector->lock
 24 *
 25 * group->mark_mutex protects the marks_list anchored inside a given group and
 26 * each mark is hooked via the g_list.  It also protects the groups private
 27 * data (i.e group limits).
 28
 29 * mark->lock protects the marks attributes like its masks and flags.
 30 * Furthermore it protects the access to a reference of the group that the mark
 31 * is assigned to as well as the access to a reference of the inode/vfsmount
 32 * that is being watched by the mark.
 33 *
 34 * mark->connector->lock protects the list of marks anchored inside an
 35 * inode / vfsmount and each mark is hooked via the i_list.
 
 36 *
 37 * A list of notification marks relating to inode / mnt is contained in
 38 * fsnotify_mark_connector. That structure is alive as long as there are any
 39 * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets
 40 * detached from fsnotify_mark_connector when last reference to the mark is
 41 * dropped.  Thus having mark reference is enough to protect mark->connector
 42 * pointer and to make sure fsnotify_mark_connector cannot disappear. Also
 43 * because we remove mark from g_list before dropping mark reference associated
 44 * with that, any mark found through g_list is guaranteed to have
 45 * mark->connector set until we drop group->mark_mutex.
 46 *
 47 * LIFETIME:
 48 * Inode marks survive between when they are added to an inode and when their
 49 * refcnt==0. Marks are also protected by fsnotify_mark_srcu.
 50 *
 51 * The inode mark can be cleared for a number of different reasons including:
 52 * - The inode is unlinked for the last time.  (fsnotify_inode_remove)
 53 * - The inode is being evicted from cache. (fsnotify_inode_delete)
 54 * - The fs the inode is on is unmounted.  (fsnotify_inode_delete/fsnotify_unmount_inodes)
 55 * - Something explicitly requests that it be removed.  (fsnotify_destroy_mark)
 56 * - The fsnotify_group associated with the mark is going away and all such marks
 57 *   need to be cleaned up. (fsnotify_clear_marks_by_group)
 58 *
 
 
 
 
 
 
 
 
 
 
 
 59 * This has the very interesting property of being able to run concurrently with
 60 * any (or all) other directions.
 61 */
 62
 63#include <linux/fs.h>
 64#include <linux/init.h>
 65#include <linux/kernel.h>
 66#include <linux/kthread.h>
 67#include <linux/module.h>
 68#include <linux/mutex.h>
 69#include <linux/slab.h>
 70#include <linux/spinlock.h>
 71#include <linux/srcu.h>
 72#include <linux/ratelimit.h>
 73
 74#include <linux/atomic.h>
 75
 76#include <linux/fsnotify_backend.h>
 77#include "fsnotify.h"
 78
 79#define FSNOTIFY_REAPER_DELAY	(1)	/* 1 jiffy */
 80
 81struct srcu_struct fsnotify_mark_srcu;
 82struct kmem_cache *fsnotify_mark_connector_cachep;
 83
 84static DEFINE_SPINLOCK(destroy_lock);
 85static LIST_HEAD(destroy_list);
 86static struct fsnotify_mark_connector *connector_destroy_list;
 87
 88static void fsnotify_mark_destroy_workfn(struct work_struct *work);
 89static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy_workfn);
 90
 91static void fsnotify_connector_destroy_workfn(struct work_struct *work);
 92static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn);
 93
 94void fsnotify_get_mark(struct fsnotify_mark *mark)
 95{
 96	WARN_ON_ONCE(!refcount_read(&mark->refcnt));
 97	refcount_inc(&mark->refcnt);
 98}
 99
100static __u32 *fsnotify_conn_mask_p(struct fsnotify_mark_connector *conn)
101{
102	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
103		return &fsnotify_conn_inode(conn)->i_fsnotify_mask;
104	else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT)
105		return &fsnotify_conn_mount(conn)->mnt_fsnotify_mask;
106	else if (conn->type == FSNOTIFY_OBJ_TYPE_SB)
107		return &fsnotify_conn_sb(conn)->s_fsnotify_mask;
108	return NULL;
109}
110
111__u32 fsnotify_conn_mask(struct fsnotify_mark_connector *conn)
112{
113	if (WARN_ON(!fsnotify_valid_obj_type(conn->type)))
114		return 0;
115
116	return *fsnotify_conn_mask_p(conn);
 
117}
118
119static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 
120{
121	u32 new_mask = 0;
122	struct fsnotify_mark *mark;
123
124	assert_spin_locked(&conn->lock);
125	/* We can get detached connector here when inode is getting unlinked. */
126	if (!fsnotify_valid_obj_type(conn->type))
127		return;
128	hlist_for_each_entry(mark, &conn->list, obj_list) {
129		if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)
130			new_mask |= mark->mask;
131	}
132	*fsnotify_conn_mask_p(conn) = new_mask;
133}
134
135/*
136 * Calculate mask of events for a list of marks. The caller must make sure
137 * connector and connector->obj cannot disappear under us.  Callers achieve
138 * this by holding a mark->lock or mark->group->mark_mutex for a mark on this
139 * list.
140 */
141void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
142{
143	if (!conn)
144		return;
145
146	spin_lock(&conn->lock);
147	__fsnotify_recalc_mask(conn);
148	spin_unlock(&conn->lock);
149	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
150		__fsnotify_update_child_dentry_flags(
151					fsnotify_conn_inode(conn));
152}
153
154/* Free all connectors queued for freeing once SRCU period ends */
155static void fsnotify_connector_destroy_workfn(struct work_struct *work)
156{
157	struct fsnotify_mark_connector *conn, *free;
158
159	spin_lock(&destroy_lock);
160	conn = connector_destroy_list;
161	connector_destroy_list = NULL;
162	spin_unlock(&destroy_lock);
163
164	synchronize_srcu(&fsnotify_mark_srcu);
165	while (conn) {
166		free = conn;
167		conn = conn->destroy_next;
168		kmem_cache_free(fsnotify_mark_connector_cachep, free);
169	}
170}
171
172static void *fsnotify_detach_connector_from_object(
173					struct fsnotify_mark_connector *conn,
174					unsigned int *type)
175{
176	struct inode *inode = NULL;
177
178	*type = conn->type;
179	if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED)
180		return NULL;
181
182	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) {
183		inode = fsnotify_conn_inode(conn);
184		inode->i_fsnotify_mask = 0;
185		atomic_long_inc(&inode->i_sb->s_fsnotify_inode_refs);
186	} else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) {
187		fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0;
188	} else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) {
189		fsnotify_conn_sb(conn)->s_fsnotify_mask = 0;
190	}
191
192	rcu_assign_pointer(*(conn->obj), NULL);
193	conn->obj = NULL;
194	conn->type = FSNOTIFY_OBJ_TYPE_DETACHED;
195
196	return inode;
197}
198
199static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark)
200{
201	struct fsnotify_group *group = mark->group;
202
203	if (WARN_ON_ONCE(!group))
204		return;
205	group->ops->free_mark(mark);
206	fsnotify_put_group(group);
207}
208
209/* Drop object reference originally held by a connector */
210static void fsnotify_drop_object(unsigned int type, void *objp)
211{
212	struct inode *inode;
213	struct super_block *sb;
214
215	if (!objp)
216		return;
217	/* Currently only inode references are passed to be dropped */
218	if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE))
219		return;
220	inode = objp;
221	sb = inode->i_sb;
222	iput(inode);
223	if (atomic_long_dec_and_test(&sb->s_fsnotify_inode_refs))
224		wake_up_var(&sb->s_fsnotify_inode_refs);
225}
226
227void fsnotify_put_mark(struct fsnotify_mark *mark)
228{
229	struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector);
230	void *objp = NULL;
231	unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED;
232	bool free_conn = false;
233
234	/* Catch marks that were actually never attached to object */
235	if (!conn) {
236		if (refcount_dec_and_test(&mark->refcnt))
237			fsnotify_final_mark_destroy(mark);
238		return;
239	}
240
241	/*
242	 * We have to be careful so that traversals of obj_list under lock can
243	 * safely grab mark reference.
244	 */
245	if (!refcount_dec_and_lock(&mark->refcnt, &conn->lock))
246		return;
247
248	hlist_del_init_rcu(&mark->obj_list);
249	if (hlist_empty(&conn->list)) {
250		objp = fsnotify_detach_connector_from_object(conn, &type);
251		free_conn = true;
252	} else {
253		__fsnotify_recalc_mask(conn);
254	}
255	WRITE_ONCE(mark->connector, NULL);
256	spin_unlock(&conn->lock);
257
258	fsnotify_drop_object(type, objp);
259
260	if (free_conn) {
261		spin_lock(&destroy_lock);
262		conn->destroy_next = connector_destroy_list;
263		connector_destroy_list = conn;
264		spin_unlock(&destroy_lock);
265		queue_work(system_unbound_wq, &connector_reaper_work);
266	}
267	/*
268	 * Note that we didn't update flags telling whether inode cares about
269	 * what's happening with children. We update these flags from
270	 * __fsnotify_parent() lazily when next event happens on one of our
271	 * children.
272	 */
273	spin_lock(&destroy_lock);
274	list_add(&mark->g_list, &destroy_list);
275	spin_unlock(&destroy_lock);
276	queue_delayed_work(system_unbound_wq, &reaper_work,
277			   FSNOTIFY_REAPER_DELAY);
278}
279EXPORT_SYMBOL_GPL(fsnotify_put_mark);
280
281/*
282 * Get mark reference when we found the mark via lockless traversal of object
283 * list. Mark can be already removed from the list by now and on its way to be
284 * destroyed once SRCU period ends.
285 *
286 * Also pin the group so it doesn't disappear under us.
287 */
288static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
289{
290	if (!mark)
291		return true;
292
293	if (refcount_inc_not_zero(&mark->refcnt)) {
294		spin_lock(&mark->lock);
295		if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
296			/* mark is attached, group is still alive then */
297			atomic_inc(&mark->group->user_waits);
298			spin_unlock(&mark->lock);
299			return true;
300		}
301		spin_unlock(&mark->lock);
302		fsnotify_put_mark(mark);
303	}
304	return false;
305}
306
307/*
308 * Puts marks and wakes up group destruction if necessary.
309 *
310 * Pairs with fsnotify_get_mark_safe()
311 */
312static void fsnotify_put_mark_wake(struct fsnotify_mark *mark)
313{
314	if (mark) {
315		struct fsnotify_group *group = mark->group;
316
317		fsnotify_put_mark(mark);
318		/*
319		 * We abuse notification_waitq on group shutdown for waiting for
320		 * all marks pinned when waiting for userspace.
321		 */
322		if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
323			wake_up(&group->notification_waitq);
324	}
325}
326
327bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
328	__releases(&fsnotify_mark_srcu)
329{
330	int type;
331
332	fsnotify_foreach_obj_type(type) {
333		/* This can fail if mark is being removed */
334		if (!fsnotify_get_mark_safe(iter_info->marks[type])) {
335			__release(&fsnotify_mark_srcu);
336			goto fail;
337		}
338	}
339
340	/*
341	 * Now that both marks are pinned by refcount in the inode / vfsmount
342	 * lists, we can drop SRCU lock, and safely resume the list iteration
343	 * once userspace returns.
344	 */
345	srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);
346
347	return true;
348
349fail:
350	for (type--; type >= 0; type--)
351		fsnotify_put_mark_wake(iter_info->marks[type]);
352	return false;
353}
354
355void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
356	__acquires(&fsnotify_mark_srcu)
357{
358	int type;
359
360	iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
361	fsnotify_foreach_obj_type(type)
362		fsnotify_put_mark_wake(iter_info->marks[type]);
363}
364
365/*
366 * Mark mark as detached, remove it from group list. Mark still stays in object
367 * list until its last reference is dropped. Note that we rely on mark being
368 * removed from group list before corresponding reference to it is dropped. In
369 * particular we rely on mark->connector being valid while we hold
370 * group->mark_mutex if we found the mark through g_list.
371 *
372 * Must be called with group->mark_mutex held. The caller must either hold
373 * reference to the mark or be protected by fsnotify_mark_srcu.
374 */
375void fsnotify_detach_mark(struct fsnotify_mark *mark)
376{
377	struct fsnotify_group *group = mark->group;
378
379	WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
380	WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
381		     refcount_read(&mark->refcnt) < 1 +
382			!!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
383
384	spin_lock(&mark->lock);
385	/* something else already called this function on this mark */
386	if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
387		spin_unlock(&mark->lock);
388		return;
389	}
390	mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
391	list_del_init(&mark->g_list);
 
392	spin_unlock(&mark->lock);
393
394	atomic_dec(&group->num_marks);
 
395
396	/* Drop mark reference acquired in fsnotify_add_mark_locked() */
397	fsnotify_put_mark(mark);
398}
399
400/*
401 * Free fsnotify mark. The mark is actually only marked as being freed.  The
402 * freeing is actually happening only once last reference to the mark is
403 * dropped from a workqueue which first waits for srcu period end.
404 *
405 * Caller must have a reference to the mark or be protected by
406 * fsnotify_mark_srcu.
407 */
408void fsnotify_free_mark(struct fsnotify_mark *mark)
409{
410	struct fsnotify_group *group = mark->group;
411
412	spin_lock(&mark->lock);
413	/* something else already called this function on this mark */
414	if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
415		spin_unlock(&mark->lock);
416		return;
417	}
418	mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
419	spin_unlock(&mark->lock);
420
 
 
 
 
 
 
421	/*
422	 * Some groups like to know that marks are being freed.  This is a
423	 * callback to the group function to let it know that this mark
424	 * is being freed.
425	 */
426	if (group->ops->freeing_mark)
427		group->ops->freeing_mark(mark, group);
428}
429
430void fsnotify_destroy_mark(struct fsnotify_mark *mark,
431			   struct fsnotify_group *group)
432{
433	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
434	fsnotify_detach_mark(mark);
435	mutex_unlock(&group->mark_mutex);
436	fsnotify_free_mark(mark);
437}
438EXPORT_SYMBOL_GPL(fsnotify_destroy_mark);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
439
440/*
441 * Sorting function for lists of fsnotify marks.
442 *
443 * Fanotify supports different notification classes (reflected as priority of
444 * notification group). Events shall be passed to notification groups in
445 * decreasing priority order. To achieve this marks in notification lists for
446 * inodes and vfsmounts are sorted so that priorities of corresponding groups
447 * are descending.
448 *
449 * Furthermore correct handling of the ignore mask requires processing inode
450 * and vfsmount marks of each group together. Using the group address as
451 * further sort criterion provides a unique sorting order and thus we can
452 * merge inode and vfsmount lists of marks in linear time and find groups
453 * present in both lists.
454 *
455 * A return value of 1 signifies that b has priority over a.
456 * A return value of 0 signifies that the two marks have to be handled together.
457 * A return value of -1 signifies that a has priority over b.
458 */
459int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
460{
461	if (a == b)
462		return 0;
463	if (!a)
464		return 1;
465	if (!b)
466		return -1;
467	if (a->priority < b->priority)
468		return 1;
469	if (a->priority > b->priority)
470		return -1;
471	if (a < b)
472		return 1;
473	return -1;
474}
475
476static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
477					       unsigned int type,
478					       __kernel_fsid_t *fsid)
479{
480	struct inode *inode = NULL;
481	struct fsnotify_mark_connector *conn;
482
483	conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);
484	if (!conn)
485		return -ENOMEM;
486	spin_lock_init(&conn->lock);
487	INIT_HLIST_HEAD(&conn->list);
488	conn->type = type;
489	conn->obj = connp;
490	/* Cache fsid of filesystem containing the object */
491	if (fsid) {
492		conn->fsid = *fsid;
493		conn->flags = FSNOTIFY_CONN_FLAG_HAS_FSID;
494	} else {
495		conn->fsid.val[0] = conn->fsid.val[1] = 0;
496		conn->flags = 0;
497	}
498	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
499		inode = igrab(fsnotify_conn_inode(conn));
500	/*
501	 * cmpxchg() provides the barrier so that readers of *connp can see
502	 * only initialized structure
503	 */
504	if (cmpxchg(connp, NULL, conn)) {
505		/* Someone else created list structure for us */
506		if (inode)
507			iput(inode);
508		kmem_cache_free(fsnotify_mark_connector_cachep, conn);
509	}
510
511	return 0;
512}
513
514/*
515 * Get mark connector, make sure it is alive and return with its lock held.
516 * This is for users that get connector pointer from inode or mount. Users that
517 * hold reference to a mark on the list may directly lock connector->lock as
518 * they are sure list cannot go away under them.
519 */
520static struct fsnotify_mark_connector *fsnotify_grab_connector(
521						fsnotify_connp_t *connp)
522{
523	struct fsnotify_mark_connector *conn;
524	int idx;
525
526	idx = srcu_read_lock(&fsnotify_mark_srcu);
527	conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
528	if (!conn)
529		goto out;
530	spin_lock(&conn->lock);
531	if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) {
532		spin_unlock(&conn->lock);
533		srcu_read_unlock(&fsnotify_mark_srcu, idx);
534		return NULL;
535	}
536out:
537	srcu_read_unlock(&fsnotify_mark_srcu, idx);
538	return conn;
539}
540
541/*
542 * Add mark into proper place in given list of marks. These marks may be used
543 * for the fsnotify backend to determine which event types should be delivered
544 * to which group and for which inodes. These marks are ordered according to
545 * priority, highest number first, and then by the group's location in memory.
546 */
547static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
548				  fsnotify_connp_t *connp, unsigned int type,
549				  int allow_dups, __kernel_fsid_t *fsid)
550{
551	struct fsnotify_mark *lmark, *last = NULL;
552	struct fsnotify_mark_connector *conn;
553	int cmp;
554	int err = 0;
555
556	if (WARN_ON(!fsnotify_valid_obj_type(type)))
557		return -EINVAL;
558
559	/* Backend is expected to check for zero fsid (e.g. tmpfs) */
560	if (fsid && WARN_ON_ONCE(!fsid->val[0] && !fsid->val[1]))
561		return -ENODEV;
562
563restart:
564	spin_lock(&mark->lock);
565	conn = fsnotify_grab_connector(connp);
566	if (!conn) {
567		spin_unlock(&mark->lock);
568		err = fsnotify_attach_connector_to_object(connp, type, fsid);
569		if (err)
570			return err;
571		goto restart;
572	} else if (fsid && !(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID)) {
573		conn->fsid = *fsid;
574		/* Pairs with smp_rmb() in fanotify_get_fsid() */
575		smp_wmb();
576		conn->flags |= FSNOTIFY_CONN_FLAG_HAS_FSID;
577	} else if (fsid && (conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID) &&
578		   (fsid->val[0] != conn->fsid.val[0] ||
579		    fsid->val[1] != conn->fsid.val[1])) {
580		/*
581		 * Backend is expected to check for non uniform fsid
582		 * (e.g. btrfs), but maybe we missed something?
583		 * Only allow setting conn->fsid once to non zero fsid.
584		 * inotify and non-fid fanotify groups do not set nor test
585		 * conn->fsid.
586		 */
587		pr_warn_ratelimited("%s: fsid mismatch on object of type %u: "
588				    "%x.%x != %x.%x\n", __func__, conn->type,
589				    fsid->val[0], fsid->val[1],
590				    conn->fsid.val[0], conn->fsid.val[1]);
591		err = -EXDEV;
592		goto out_err;
593	}
594
595	/* is mark the first mark? */
596	if (hlist_empty(&conn->list)) {
597		hlist_add_head_rcu(&mark->obj_list, &conn->list);
598		goto added;
599	}
600
601	/* should mark be in the middle of the current list? */
602	hlist_for_each_entry(lmark, &conn->list, obj_list) {
603		last = lmark;
604
605		if ((lmark->group == mark->group) &&
606		    (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) &&
607		    !allow_dups) {
608			err = -EEXIST;
609			goto out_err;
610		}
611
612		cmp = fsnotify_compare_groups(lmark->group, mark->group);
613		if (cmp >= 0) {
614			hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
615			goto added;
616		}
617	}
618
619	BUG_ON(last == NULL);
620	/* mark should be the last entry.  last is the current last entry */
621	hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
622added:
623	/*
624	 * Since connector is attached to object using cmpxchg() we are
625	 * guaranteed that connector initialization is fully visible by anyone
626	 * seeing mark->connector set.
627	 */
628	WRITE_ONCE(mark->connector, conn);
629out_err:
630	spin_unlock(&conn->lock);
631	spin_unlock(&mark->lock);
632	return err;
633}
634
635/*
636 * Attach an initialized mark to a given group and fs object.
637 * These marks may be used for the fsnotify backend to determine which
638 * event types should be delivered to which group.
639 */
640int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
641			     fsnotify_connp_t *connp, unsigned int type,
642			     int allow_dups, __kernel_fsid_t *fsid)
643{
644	struct fsnotify_group *group = mark->group;
645	int ret = 0;
646
 
 
647	BUG_ON(!mutex_is_locked(&group->mark_mutex));
648
649	/*
650	 * LOCKING ORDER!!!!
651	 * group->mark_mutex
652	 * mark->lock
653	 * mark->connector->lock
654	 */
655	spin_lock(&mark->lock);
656	mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
657
 
 
658	list_add(&mark->g_list, &group->marks_list);
659	atomic_inc(&group->num_marks);
660	fsnotify_get_mark(mark); /* for g_list */
661	spin_unlock(&mark->lock);
662
663	ret = fsnotify_add_mark_list(mark, connp, type, allow_dups, fsid);
664	if (ret)
665		goto err;
 
 
 
 
 
 
 
 
 
 
 
 
666
667	if (mark->mask)
668		fsnotify_recalc_mask(mark->connector);
669
670	return ret;
671err:
672	spin_lock(&mark->lock);
673	mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE |
674			 FSNOTIFY_MARK_FLAG_ATTACHED);
675	list_del_init(&mark->g_list);
676	spin_unlock(&mark->lock);
 
677	atomic_dec(&group->num_marks);
678
679	fsnotify_put_mark(mark);
 
 
 
 
 
 
 
680	return ret;
681}
682
683int fsnotify_add_mark(struct fsnotify_mark *mark, fsnotify_connp_t *connp,
684		      unsigned int type, int allow_dups, __kernel_fsid_t *fsid)
685{
686	int ret;
687	struct fsnotify_group *group = mark->group;
688
689	mutex_lock(&group->mark_mutex);
690	ret = fsnotify_add_mark_locked(mark, connp, type, allow_dups, fsid);
691	mutex_unlock(&group->mark_mutex);
692	return ret;
693}
694EXPORT_SYMBOL_GPL(fsnotify_add_mark);
695
696/*
697 * Given a list of marks, find the mark associated with given group. If found
698 * take a reference to that mark and return it, else return NULL.
699 */
700struct fsnotify_mark *fsnotify_find_mark(fsnotify_connp_t *connp,
701					 struct fsnotify_group *group)
702{
703	struct fsnotify_mark_connector *conn;
704	struct fsnotify_mark *mark;
705
706	conn = fsnotify_grab_connector(connp);
707	if (!conn)
708		return NULL;
709
710	hlist_for_each_entry(mark, &conn->list, obj_list) {
711		if (mark->group == group &&
712		    (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
713			fsnotify_get_mark(mark);
714			spin_unlock(&conn->lock);
715			return mark;
716		}
717	}
718	spin_unlock(&conn->lock);
719	return NULL;
720}
721EXPORT_SYMBOL_GPL(fsnotify_find_mark);
722
723/* Clear any marks in a group with given type mask */
724void fsnotify_clear_marks_by_group(struct fsnotify_group *group,
725				   unsigned int type_mask)
 
 
726{
727	struct fsnotify_mark *lmark, *mark;
728	LIST_HEAD(to_free);
729	struct list_head *head = &to_free;
730
731	/* Skip selection step if we want to clear all marks. */
732	if (type_mask == FSNOTIFY_OBJ_ALL_TYPES_MASK) {
733		head = &group->marks_list;
734		goto clear;
735	}
736	/*
737	 * We have to be really careful here. Anytime we drop mark_mutex, e.g.
738	 * fsnotify_clear_marks_by_inode() can come and free marks. Even in our
739	 * to_free list so we have to use mark_mutex even when accessing that
740	 * list. And freeing mark requires us to drop mark_mutex. So we can
741	 * reliably free only the first mark in the list. That's why we first
742	 * move marks to free to to_free list in one go and then free marks in
743	 * to_free list one by one.
744	 */
745	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
746	list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
747		if ((1U << mark->connector->type) & type_mask)
748			list_move(&mark->g_list, &to_free);
749	}
750	mutex_unlock(&group->mark_mutex);
751
752clear:
753	while (1) {
754		mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
755		if (list_empty(head)) {
756			mutex_unlock(&group->mark_mutex);
757			break;
758		}
759		mark = list_first_entry(head, struct fsnotify_mark, g_list);
760		fsnotify_get_mark(mark);
761		fsnotify_detach_mark(mark);
762		mutex_unlock(&group->mark_mutex);
763		fsnotify_free_mark(mark);
764		fsnotify_put_mark(mark);
765	}
766}
767
768/* Destroy all marks attached to an object via connector */
769void fsnotify_destroy_marks(fsnotify_connp_t *connp)
 
 
770{
771	struct fsnotify_mark_connector *conn;
772	struct fsnotify_mark *mark, *old_mark = NULL;
773	void *objp;
774	unsigned int type;
775
776	conn = fsnotify_grab_connector(connp);
777	if (!conn)
778		return;
779	/*
780	 * We have to be careful since we can race with e.g.
781	 * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the
782	 * list can get modified. However we are holding mark reference and
783	 * thus our mark cannot be removed from obj_list so we can continue
784	 * iteration after regaining conn->lock.
785	 */
786	hlist_for_each_entry(mark, &conn->list, obj_list) {
787		fsnotify_get_mark(mark);
788		spin_unlock(&conn->lock);
789		if (old_mark)
790			fsnotify_put_mark(old_mark);
791		old_mark = mark;
792		fsnotify_destroy_mark(mark, mark->group);
793		spin_lock(&conn->lock);
794	}
795	/*
796	 * Detach list from object now so that we don't pin inode until all
797	 * mark references get dropped. It would lead to strange results such
798	 * as delaying inode deletion or blocking unmount.
799	 */
800	objp = fsnotify_detach_connector_from_object(conn, &type);
801	spin_unlock(&conn->lock);
802	if (old_mark)
803		fsnotify_put_mark(old_mark);
804	fsnotify_drop_object(type, objp);
805}
806
807/*
808 * Nothing fancy, just initialize lists and locks and counters.
809 */
810void fsnotify_init_mark(struct fsnotify_mark *mark,
811			struct fsnotify_group *group)
812{
813	memset(mark, 0, sizeof(*mark));
814	spin_lock_init(&mark->lock);
815	refcount_set(&mark->refcnt, 1);
816	fsnotify_get_group(group);
817	mark->group = group;
818	WRITE_ONCE(mark->connector, NULL);
819}
820EXPORT_SYMBOL_GPL(fsnotify_init_mark);
821
822/*
823 * Destroy all marks in destroy_list, waits for SRCU period to finish before
824 * actually freeing marks.
825 */
826static void fsnotify_mark_destroy_workfn(struct work_struct *work)
827{
828	struct fsnotify_mark *mark, *next;
829	struct list_head private_destroy_list;
830
831	spin_lock(&destroy_lock);
832	/* exchange the list head */
833	list_replace_init(&destroy_list, &private_destroy_list);
834	spin_unlock(&destroy_lock);
835
836	synchronize_srcu(&fsnotify_mark_srcu);
837
838	list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
839		list_del_init(&mark->g_list);
840		fsnotify_final_mark_destroy(mark);
841	}
842}
843
844/* Wait for all marks queued for destruction to be actually destroyed */
845void fsnotify_wait_marks_destroyed(void)
846{
847	flush_delayed_work(&reaper_work);
848}
849EXPORT_SYMBOL_GPL(fsnotify_wait_marks_destroyed);