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 */
fsnotify_final_destroy_group(struct fsnotify_group * group)22 static 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 */
fsnotify_group_stop_queueing(struct fsnotify_group * group)37 void 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 */
fsnotify_destroy_group(struct fsnotify_group * group)50 void 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 */
fsnotify_get_group(struct fsnotify_group * group)99 void 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 */
fsnotify_put_group(struct fsnotify_group * group)107 void fsnotify_put_group(struct fsnotify_group *group)
108 {
109 if (refcount_dec_and_test(&group->refcnt))
110 fsnotify_final_destroy_group(group);
111 }
112 EXPORT_SYMBOL_GPL(fsnotify_put_group);
113
__fsnotify_alloc_group(const struct fsnotify_ops * ops,int flags,gfp_t gfp)114 static 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 */
fsnotify_alloc_group(const struct fsnotify_ops * ops,int flags)156 struct 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 }
164 EXPORT_SYMBOL_GPL(fsnotify_alloc_group);
165
fsnotify_fasync(int fd,struct file * file,int on)166 int 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