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#include <linux/list.h>
7#include <linux/mutex.h>
8#include <linux/slab.h>
9#include <linux/srcu.h>
10#include <linux/rculist.h>
11#include <linux/wait.h>
12#include <linux/memcontrol.h>
13
14#include <linux/fsnotify_backend.h>
15#include "fsnotify.h"
16
17#include <linux/atomic.h>
18
19/*
20 * Final freeing of a group
21 */
22static void fsnotify_final_destroy_group(struct fsnotify_group *group)
23{
24	if (group->ops->free_group_priv)
25		group->ops->free_group_priv(group);
26
27	mem_cgroup_put(group->memcg);
28	mutex_destroy(&group->mark_mutex);
29
30	kfree(group);
31}
32
33/*
34 * Stop queueing new events for this group. Once this function returns
35 * fsnotify_add_event() will not add any new events to the group's queue.
36 */
37void fsnotify_group_stop_queueing(struct fsnotify_group *group)
38{
39	spin_lock(&group->notification_lock);
40	group->shutdown = true;
41	spin_unlock(&group->notification_lock);
42}
43
44/*
45 * Trying to get rid of a group. Remove all marks, flush all events and release
46 * the group reference.
47 * Note that another thread calling fsnotify_clear_marks_by_group() may still
48 * hold a ref to the group.
49 */
50void fsnotify_destroy_group(struct fsnotify_group *group)
51{
52	/*
53	 * Stop queueing new events. The code below is careful enough to not
54	 * require this but fanotify needs to stop queuing events even before
55	 * fsnotify_destroy_group() is called and this makes the other callers
56	 * of fsnotify_destroy_group() to see the same behavior.
57	 */
58	fsnotify_group_stop_queueing(group);
59
60	/* Clear all marks for this group and queue them for destruction */
61	fsnotify_clear_marks_by_group(group, FSNOTIFY_OBJ_TYPE_ANY);
62
63	/*
64	 * Some marks can still be pinned when waiting for response from
65	 * userspace. Wait for those now. fsnotify_prepare_user_wait() will
66	 * not succeed now so this wait is race-free.
67	 */
68	wait_event(group->notification_waitq, !atomic_read(&group->user_waits));
69
70	/*
71	 * Wait until all marks get really destroyed. We could actually destroy
72	 * them ourselves instead of waiting for worker to do it, however that
73	 * would be racy as worker can already be processing some marks before
74	 * we even entered fsnotify_destroy_group().
75	 */
76	fsnotify_wait_marks_destroyed();
77
78	/*
79	 * Since we have waited for fsnotify_mark_srcu in
80	 * fsnotify_mark_destroy_list() there can be no outstanding event
81	 * notification against this group. So clearing the notification queue
82	 * of all events is reliable now.
83	 */
84	fsnotify_flush_notify(group);
85
86	/*
87	 * Destroy overflow event (we cannot use fsnotify_destroy_event() as
88	 * that deliberately ignores overflow events.
89	 */
90	if (group->overflow_event)
91		group->ops->free_event(group, group->overflow_event);
92
93	fsnotify_put_group(group);
94}
95
96/*
97 * Get reference to a group.
98 */
99void fsnotify_get_group(struct fsnotify_group *group)
100{
101	refcount_inc(&group->refcnt);
102}
103
104/*
105 * Drop a reference to a group.  Free it if it's through.
106 */
107void fsnotify_put_group(struct fsnotify_group *group)
108{
109	if (refcount_dec_and_test(&group->refcnt))
110		fsnotify_final_destroy_group(group);
111}
112EXPORT_SYMBOL_GPL(fsnotify_put_group);
113
114static struct fsnotify_group *__fsnotify_alloc_group(
115				const struct fsnotify_ops *ops,
116				int flags, gfp_t gfp)
117{
118	static struct lock_class_key nofs_marks_lock;
119	struct fsnotify_group *group;
120
121	group = kzalloc(sizeof(struct fsnotify_group), gfp);
122	if (!group)
123		return ERR_PTR(-ENOMEM);
124
125	/* set to 0 when there a no external references to this group */
126	refcount_set(&group->refcnt, 1);
127	atomic_set(&group->user_waits, 0);
128
129	spin_lock_init(&group->notification_lock);
130	INIT_LIST_HEAD(&group->notification_list);
131	init_waitqueue_head(&group->notification_waitq);
132	group->max_events = UINT_MAX;
133
134	mutex_init(&group->mark_mutex);
135	INIT_LIST_HEAD(&group->marks_list);
136
137	group->ops = ops;
138	group->flags = flags;
139	/*
140	 * For most backends, eviction of inode with a mark is not expected,
141	 * because marks hold a refcount on the inode against eviction.
142	 *
143	 * Use a different lockdep class for groups that support evictable
144	 * inode marks, because with evictable marks, mark_mutex is NOT
145	 * fs-reclaim safe - the mutex is taken when evicting inodes.
146	 */
147	if (flags & FSNOTIFY_GROUP_NOFS)
148		lockdep_set_class(&group->mark_mutex, &nofs_marks_lock);
149
150	return group;
151}
152
153/*
154 * Create a new fsnotify_group and hold a reference for the group returned.
155 */
156struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops,
157					    int flags)
158{
159	gfp_t gfp = (flags & FSNOTIFY_GROUP_USER) ? GFP_KERNEL_ACCOUNT :
160						    GFP_KERNEL;
161
162	return __fsnotify_alloc_group(ops, flags, gfp);
163}
164EXPORT_SYMBOL_GPL(fsnotify_alloc_group);
165
166int fsnotify_fasync(int fd, struct file *file, int on)
167{
168	struct fsnotify_group *group = file->private_data;
169
170	return fasync_helper(fd, file, on, &group->fsn_fa) >= 0 ? 0 : -EIO;
171}
172