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![Eric Paris](/assets/img/avatar_default.png)
In f44aebcc
the tail drop logic of events with no file backing
(q_overflow and in_ignored) was reversed so IN_IGNORED events would
never be tail dropped. This now means that Q_OVERFLOW events are NOT
tail dropped. The fix is to not tail drop IN_IGNORED, but to tail drop
Q_OVERFLOW.
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
421 lines
12 KiB
C
421 lines
12 KiB
C
/*
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* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*
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* Basic idea behind the notification queue: An fsnotify group (like inotify)
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* sends the userspace notification about events asyncronously some time after
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* the event happened. When inotify gets an event it will need to add that
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* event to the group notify queue. Since a single event might need to be on
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* multiple group's notification queues we can't add the event directly to each
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* queue and instead add a small "event_holder" to each queue. This event_holder
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* has a pointer back to the original event. Since the majority of events are
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* going to end up on one, and only one, notification queue we embed one
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* event_holder into each event. This means we have a single allocation instead
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* of always needing two. If the embedded event_holder is already in use by
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* another group a new event_holder (from fsnotify_event_holder_cachep) will be
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* allocated and used.
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*/
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/list.h>
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#include <linux/module.h>
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#include <linux/mount.h>
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#include <linux/mutex.h>
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#include <linux/namei.h>
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#include <linux/path.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <asm/atomic.h>
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#include <linux/fsnotify_backend.h>
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#include "fsnotify.h"
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static struct kmem_cache *fsnotify_event_cachep;
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static struct kmem_cache *fsnotify_event_holder_cachep;
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/*
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* This is a magic event we send when the q is too full. Since it doesn't
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* hold real event information we just keep one system wide and use it any time
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* it is needed. It's refcnt is set 1 at kernel init time and will never
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* get set to 0 so it will never get 'freed'
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*/
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static struct fsnotify_event q_overflow_event;
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static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
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/**
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* fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
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* Called from fsnotify_move, which is inlined into filesystem modules.
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*/
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u32 fsnotify_get_cookie(void)
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{
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return atomic_inc_return(&fsnotify_sync_cookie);
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}
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EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
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/* return true if the notify queue is empty, false otherwise */
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bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
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{
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BUG_ON(!mutex_is_locked(&group->notification_mutex));
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return list_empty(&group->notification_list) ? true : false;
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}
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void fsnotify_get_event(struct fsnotify_event *event)
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{
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atomic_inc(&event->refcnt);
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}
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void fsnotify_put_event(struct fsnotify_event *event)
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{
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if (!event)
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return;
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if (atomic_dec_and_test(&event->refcnt)) {
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if (event->data_type == FSNOTIFY_EVENT_PATH)
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path_put(&event->path);
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BUG_ON(!list_empty(&event->private_data_list));
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kfree(event->file_name);
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kmem_cache_free(fsnotify_event_cachep, event);
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}
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}
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struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
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{
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return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
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}
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void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
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{
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kmem_cache_free(fsnotify_event_holder_cachep, holder);
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}
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/*
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* Find the private data that the group previously attached to this event when
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* the group added the event to the notification queue (fsnotify_add_notify_event)
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*/
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struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
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{
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struct fsnotify_event_private_data *lpriv;
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struct fsnotify_event_private_data *priv = NULL;
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assert_spin_locked(&event->lock);
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list_for_each_entry(lpriv, &event->private_data_list, event_list) {
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if (lpriv->group == group) {
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priv = lpriv;
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list_del(&priv->event_list);
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break;
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}
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}
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return priv;
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}
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/*
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* Check if 2 events contain the same information. We do not compare private data
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* but at this moment that isn't a problem for any know fsnotify listeners.
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*/
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static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
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{
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if ((old->mask == new->mask) &&
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(old->to_tell == new->to_tell) &&
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(old->data_type == new->data_type) &&
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(old->name_len == new->name_len)) {
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switch (old->data_type) {
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case (FSNOTIFY_EVENT_INODE):
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/* remember, after old was put on the wait_q we aren't
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* allowed to look at the inode any more, only thing
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* left to check was if the file_name is the same */
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if (old->name_len &&
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!strcmp(old->file_name, new->file_name))
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return true;
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break;
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case (FSNOTIFY_EVENT_PATH):
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if ((old->path.mnt == new->path.mnt) &&
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(old->path.dentry == new->path.dentry))
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return true;
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break;
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case (FSNOTIFY_EVENT_NONE):
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if (old->mask & FS_Q_OVERFLOW)
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return true;
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else if (old->mask & FS_IN_IGNORED)
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return false;
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return false;
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};
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}
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return false;
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}
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/*
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* Add an event to the group notification queue. The group can later pull this
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* event off the queue to deal with. If the event is successfully added to the
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* group's notification queue, a reference is taken on event.
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*/
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int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
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struct fsnotify_event_private_data *priv)
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{
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struct fsnotify_event_holder *holder = NULL;
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struct list_head *list = &group->notification_list;
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struct fsnotify_event_holder *last_holder;
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struct fsnotify_event *last_event;
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int ret = 0;
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/*
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* There is one fsnotify_event_holder embedded inside each fsnotify_event.
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* Check if we expect to be able to use that holder. If not alloc a new
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* holder.
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* For the overflow event it's possible that something will use the in
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* event holder before we get the lock so we may need to jump back and
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* alloc a new holder, this can't happen for most events...
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*/
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if (!list_empty(&event->holder.event_list)) {
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alloc_holder:
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holder = fsnotify_alloc_event_holder();
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if (!holder)
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return -ENOMEM;
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}
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mutex_lock(&group->notification_mutex);
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if (group->q_len >= group->max_events) {
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event = &q_overflow_event;
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ret = -EOVERFLOW;
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/* sorry, no private data on the overflow event */
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priv = NULL;
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}
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spin_lock(&event->lock);
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if (list_empty(&event->holder.event_list)) {
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if (unlikely(holder))
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fsnotify_destroy_event_holder(holder);
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holder = &event->holder;
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} else if (unlikely(!holder)) {
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/* between the time we checked above and got the lock the in
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* event holder was used, go back and get a new one */
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spin_unlock(&event->lock);
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mutex_unlock(&group->notification_mutex);
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goto alloc_holder;
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}
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if (!list_empty(list)) {
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last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list);
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last_event = last_holder->event;
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if (event_compare(last_event, event)) {
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spin_unlock(&event->lock);
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mutex_unlock(&group->notification_mutex);
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if (holder != &event->holder)
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fsnotify_destroy_event_holder(holder);
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return -EEXIST;
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}
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}
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group->q_len++;
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holder->event = event;
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fsnotify_get_event(event);
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list_add_tail(&holder->event_list, list);
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if (priv)
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list_add_tail(&priv->event_list, &event->private_data_list);
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spin_unlock(&event->lock);
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mutex_unlock(&group->notification_mutex);
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wake_up(&group->notification_waitq);
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return ret;
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}
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/*
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* Remove and return the first event from the notification list. There is a
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* reference held on this event since it was on the list. It is the responsibility
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* of the caller to drop this reference.
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*/
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struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
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{
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struct fsnotify_event *event;
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struct fsnotify_event_holder *holder;
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BUG_ON(!mutex_is_locked(&group->notification_mutex));
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holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
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event = holder->event;
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spin_lock(&event->lock);
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holder->event = NULL;
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list_del_init(&holder->event_list);
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spin_unlock(&event->lock);
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/* event == holder means we are referenced through the in event holder */
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if (holder != &event->holder)
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fsnotify_destroy_event_holder(holder);
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group->q_len--;
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return event;
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}
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/*
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* This will not remove the event, that must be done with fsnotify_remove_notify_event()
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*/
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struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
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{
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struct fsnotify_event *event;
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struct fsnotify_event_holder *holder;
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BUG_ON(!mutex_is_locked(&group->notification_mutex));
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holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
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event = holder->event;
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return event;
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}
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/*
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* Called when a group is being torn down to clean up any outstanding
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* event notifications.
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*/
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void fsnotify_flush_notify(struct fsnotify_group *group)
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{
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struct fsnotify_event *event;
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struct fsnotify_event_private_data *priv;
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mutex_lock(&group->notification_mutex);
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while (!fsnotify_notify_queue_is_empty(group)) {
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event = fsnotify_remove_notify_event(group);
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/* if they don't implement free_event_priv they better not have attached any */
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if (group->ops->free_event_priv) {
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spin_lock(&event->lock);
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priv = fsnotify_remove_priv_from_event(group, event);
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spin_unlock(&event->lock);
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if (priv)
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group->ops->free_event_priv(priv);
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}
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fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
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}
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mutex_unlock(&group->notification_mutex);
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}
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static void initialize_event(struct fsnotify_event *event)
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{
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event->holder.event = NULL;
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INIT_LIST_HEAD(&event->holder.event_list);
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atomic_set(&event->refcnt, 1);
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spin_lock_init(&event->lock);
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event->path.dentry = NULL;
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event->path.mnt = NULL;
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event->inode = NULL;
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event->data_type = FSNOTIFY_EVENT_NONE;
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INIT_LIST_HEAD(&event->private_data_list);
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event->to_tell = NULL;
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event->file_name = NULL;
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event->name_len = 0;
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event->sync_cookie = 0;
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}
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/*
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* fsnotify_create_event - Allocate a new event which will be sent to each
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* group's handle_event function if the group was interested in this
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* particular event.
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*
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* @to_tell the inode which is supposed to receive the event (sometimes a
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* parent of the inode to which the event happened.
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* @mask what actually happened.
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* @data pointer to the object which was actually affected
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* @data_type flag indication if the data is a file, path, inode, nothing...
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* @name the filename, if available
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*/
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struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
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int data_type, const char *name, u32 cookie,
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gfp_t gfp)
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{
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struct fsnotify_event *event;
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event = kmem_cache_alloc(fsnotify_event_cachep, gfp);
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if (!event)
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return NULL;
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initialize_event(event);
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if (name) {
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event->file_name = kstrdup(name, gfp);
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if (!event->file_name) {
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kmem_cache_free(fsnotify_event_cachep, event);
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return NULL;
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}
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event->name_len = strlen(event->file_name);
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}
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event->sync_cookie = cookie;
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event->to_tell = to_tell;
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switch (data_type) {
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case FSNOTIFY_EVENT_FILE: {
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struct file *file = data;
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struct path *path = &file->f_path;
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event->path.dentry = path->dentry;
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event->path.mnt = path->mnt;
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path_get(&event->path);
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event->data_type = FSNOTIFY_EVENT_PATH;
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break;
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}
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case FSNOTIFY_EVENT_PATH: {
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struct path *path = data;
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event->path.dentry = path->dentry;
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event->path.mnt = path->mnt;
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path_get(&event->path);
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event->data_type = FSNOTIFY_EVENT_PATH;
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break;
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}
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case FSNOTIFY_EVENT_INODE:
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event->inode = data;
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event->data_type = FSNOTIFY_EVENT_INODE;
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break;
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case FSNOTIFY_EVENT_NONE:
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event->inode = NULL;
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event->path.dentry = NULL;
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event->path.mnt = NULL;
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break;
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default:
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BUG();
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}
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event->mask = mask;
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return event;
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}
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__init int fsnotify_notification_init(void)
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{
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fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
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fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
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initialize_event(&q_overflow_event);
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q_overflow_event.mask = FS_Q_OVERFLOW;
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return 0;
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}
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subsys_initcall(fsnotify_notification_init);
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