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         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  */
  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  */
  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  */
  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  */
 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
 114 static struct fsnotify_group *__fsnotify_alloc_group(
 115                                 const struct fsnotify_ops *ops,
 116                                 int flags, gfp_t gfp)
 117 {
 118         struct fsnotify_group *group;
 119
 120         group = kzalloc(sizeof(struct fsnotify_group), gfp);
 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->user_waits, 0);
 127
 128         spin_lock_init(&group->notification_lock);
 129         INIT_LIST_HEAD(&group->notification_list);
 130         init_waitqueue_head(&group->notification_waitq);
 131         group->max_events = UINT_MAX;
 132
 133         mutex_init(&group->mark_mutex);
 134         INIT_LIST_HEAD(&group->marks_list);
 135
 136         group->ops = ops;
 137         group->flags = flags;
 138
 139         return group;
 140 }
 141
 142 /*
 143  * Create a new fsnotify_group and hold a reference for the group returned.
 144  */
 145 struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops,
 146                                             int flags)
 147 {
 148         gfp_t gfp = (flags & FSNOTIFY_GROUP_USER) ? GFP_KERNEL_ACCOUNT :
 149                                                     GFP_KERNEL;
 150
 151         return __fsnotify_alloc_group(ops, flags, gfp);
 152 }
 153 EXPORT_SYMBOL_GPL(fsnotify_alloc_group);
 154
 155 int fsnotify_fasync(int fd, struct file *file, int on)
 156 {
 157         struct fsnotify_group *group = file->private_data;
 158
 159         return fasync_helper(fd, file, on, &group->fsn_fa) >= 0 ? 0 : -EIO;
 160 }