fs/notify/group.c

   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  */
  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
  29         kfree(group);
  30 }
  31
  32 /*
  33  * Stop queueing new events for this group. Once this function returns
  34  * fsnotify_add_event() will not add any new events to the group's queue.
  35  */
  36 void fsnotify_group_stop_queueing(struct fsnotify_group *group)
  37 {
  38         spin_lock(&group->notification_lock);
  39         group->shutdown = true;
  40         spin_unlock(&group->notification_lock);
  41 }
  42
  43 /*
  44  * Trying to get rid of a group. Remove all marks, flush all events and release
  45  * the group reference.
  46  * Note that another thread calling fsnotify_clear_marks_by_group() may still
  47  * hold a ref to the group.
  48  */
  49 void fsnotify_destroy_group(struct fsnotify_group *group)
  50 {
  51         /*
  52          * Stop queueing new events. The code below is careful enough to not
  53          * require this but fanotify needs to stop queuing events even before
  54          * fsnotify_destroy_group() is called and this makes the other callers
  55          * of fsnotify_destroy_group() to see the same behavior.
  56          */
  57         fsnotify_group_stop_queueing(group);
  58
  59         /* Clear all marks for this group and queue them for destruction */
  60         fsnotify_clear_marks_by_group(group, FSNOTIFY_OBJ_ALL_TYPES_MASK);
  61
  62         /*
  63          * Some marks can still be pinned when waiting for response from
  64          * userspace. Wait for those now. fsnotify_prepare_user_wait() will
  65          * not succeed now so this wait is race-free.
  66          */
  67         wait_event(group->notification_waitq, !atomic_read(&group->user_waits));
  68
  69         /*
  70          * Wait until all marks get really destroyed. We could actually destroy
  71          * them ourselves instead of waiting for worker to do it, however that
  72          * would be racy as worker can already be processing some marks before
  73          * we even entered fsnotify_destroy_group().
  74          */
  75         fsnotify_wait_marks_destroyed();
  76
  77         /*
  78          * Since we have waited for fsnotify_mark_srcu in
  79          * fsnotify_mark_destroy_list() there can be no outstanding event
  80          * notification against this group. So clearing the notification queue
  81          * of all events is reliable now.
  82          */
  83         fsnotify_flush_notify(group);
  84
  85         /*
  86          * Destroy overflow event (we cannot use fsnotify_destroy_event() as
  87          * that deliberately ignores overflow events.
  88          */
  89         if (group->overflow_event)
  90                 group->ops->free_event(group->overflow_event);
  91
  92         fsnotify_put_group(group);
  93 }
  94
  95 /*
  96  * Get reference to a group.
  97  */
  98 void fsnotify_get_group(struct fsnotify_group *group)
  99 {
 100         refcount_inc(&group->refcnt);
 101 }
 102
 103 /*
 104  * Drop a reference to a group.  Free it if it's through.
 105  */
 106 void fsnotify_put_group(struct fsnotify_group *group)
 107 {
 108         if (refcount_dec_and_test(&group->refcnt))
 109                 fsnotify_final_destroy_group(group);
 110 }
 111 EXPORT_SYMBOL_GPL(fsnotify_put_group);
 112
 113 /*
 114  * Create a new fsnotify_group and hold a reference for the group returned.
 115  */
 116 struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
 117 {
 118         struct fsnotify_group *group;
 119
 120         group = kzalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
 121         if (!group)
 122                 return ERR_PTR(-ENOMEM);
 123
 124         /* set to 0 when there a no external references to this group */
 125         refcount_set(&group->refcnt, 1);
 126         atomic_set(&group->num_marks, 0);
 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
 139         return group;
 140 }
 141 EXPORT_SYMBOL_GPL(fsnotify_alloc_group);
 142
 143 int fsnotify_fasync(int fd, struct file *file, int on)
 144 {
 145         struct fsnotify_group *group = file->private_data;
 146
 147         return fasync_helper(fd, file, on, &group->fsn_fa) >= 0 ? 0 : -EIO;
 148 }