linux/fs/notify/notification.c
Linus Torvalds 96680d2b91 Merge branch 'for-next' of git://git.infradead.org/users/eparis/notify
Pull filesystem notification updates from Eric Paris:
 "This pull mostly is about locking changes in the fsnotify system.  By
  switching the group lock from a spin_lock() to a mutex() we can now
  hold the lock across things like iput().  This fixes a problem
  involving unmounting a fs and having inodes be busy, first pointed out
  by FAT, but reproducible with tmpfs.

  This also restores signal driven I/O for inotify, which has been
  broken since about 2.6.32."

Ugh.  I *hate* the timing of this.  It was rebased after the merge
window opened, and then left to sit with the pull request coming the day
before the merge window closes.  That's just crap.  But apparently the
patches themselves have been around for over a year, just gathering
dust, so now it's suddenly critical.

Fixed up semantic conflict in fs/notify/fdinfo.c as per Stephen
Rothwell's fixes from -next.

* 'for-next' of git://git.infradead.org/users/eparis/notify:
  inotify: automatically restart syscalls
  inotify: dont skip removal of watch descriptor if creation of ignored event failed
  fanotify: dont merge permission events
  fsnotify: make fasync generic for both inotify and fanotify
  fsnotify: change locking order
  fsnotify: dont put marks on temporary list when clearing marks by group
  fsnotify: introduce locked versions of fsnotify_add_mark() and fsnotify_remove_mark()
  fsnotify: pass group to fsnotify_destroy_mark()
  fsnotify: use a mutex instead of a spinlock to protect a groups mark list
  fanotify: add an extra flag to mark_remove_from_mask that indicates wheather a mark should be destroyed
  fsnotify: take groups mark_lock before mark lock
  fsnotify: use reference counting for groups
  fsnotify: introduce fsnotify_get_group()
  inotify, fanotify: replace fsnotify_put_group() with fsnotify_destroy_group()
2012-12-20 20:11:52 -08:00

465 lines
13 KiB
C

/*
* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; see the file COPYING. If not, write to
* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* Basic idea behind the notification queue: An fsnotify group (like inotify)
* sends the userspace notification about events asynchronously some time after
* the event happened. When inotify gets an event it will need to add that
* event to the group notify queue. Since a single event might need to be on
* multiple group's notification queues we can't add the event directly to each
* queue and instead add a small "event_holder" to each queue. This event_holder
* has a pointer back to the original event. Since the majority of events are
* going to end up on one, and only one, notification queue we embed one
* event_holder into each event. This means we have a single allocation instead
* of always needing two. If the embedded event_holder is already in use by
* another group a new event_holder (from fsnotify_event_holder_cachep) will be
* allocated and used.
*/
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/mutex.h>
#include <linux/namei.h>
#include <linux/path.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/atomic.h>
#include <linux/fsnotify_backend.h>
#include "fsnotify.h"
static struct kmem_cache *fsnotify_event_cachep;
static struct kmem_cache *fsnotify_event_holder_cachep;
/*
* This is a magic event we send when the q is too full. Since it doesn't
* hold real event information we just keep one system wide and use it any time
* it is needed. It's refcnt is set 1 at kernel init time and will never
* get set to 0 so it will never get 'freed'
*/
static struct fsnotify_event *q_overflow_event;
static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
/**
* fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
* Called from fsnotify_move, which is inlined into filesystem modules.
*/
u32 fsnotify_get_cookie(void)
{
return atomic_inc_return(&fsnotify_sync_cookie);
}
EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
/* return true if the notify queue is empty, false otherwise */
bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
{
BUG_ON(!mutex_is_locked(&group->notification_mutex));
return list_empty(&group->notification_list) ? true : false;
}
void fsnotify_get_event(struct fsnotify_event *event)
{
atomic_inc(&event->refcnt);
}
void fsnotify_put_event(struct fsnotify_event *event)
{
if (!event)
return;
if (atomic_dec_and_test(&event->refcnt)) {
pr_debug("%s: event=%p\n", __func__, event);
if (event->data_type == FSNOTIFY_EVENT_PATH)
path_put(&event->path);
BUG_ON(!list_empty(&event->private_data_list));
kfree(event->file_name);
put_pid(event->tgid);
kmem_cache_free(fsnotify_event_cachep, event);
}
}
struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
{
return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
}
void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
{
if (holder)
kmem_cache_free(fsnotify_event_holder_cachep, holder);
}
/*
* Find the private data that the group previously attached to this event when
* the group added the event to the notification queue (fsnotify_add_notify_event)
*/
struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
{
struct fsnotify_event_private_data *lpriv;
struct fsnotify_event_private_data *priv = NULL;
assert_spin_locked(&event->lock);
list_for_each_entry(lpriv, &event->private_data_list, event_list) {
if (lpriv->group == group) {
priv = lpriv;
list_del(&priv->event_list);
break;
}
}
return priv;
}
/*
* Add an event to the group notification queue. The group can later pull this
* event off the queue to deal with. If the event is successfully added to the
* group's notification queue, a reference is taken on event.
*/
struct fsnotify_event *fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
struct fsnotify_event_private_data *priv,
struct fsnotify_event *(*merge)(struct list_head *,
struct fsnotify_event *))
{
struct fsnotify_event *return_event = NULL;
struct fsnotify_event_holder *holder = NULL;
struct list_head *list = &group->notification_list;
pr_debug("%s: group=%p event=%p priv=%p\n", __func__, group, event, priv);
/*
* There is one fsnotify_event_holder embedded inside each fsnotify_event.
* Check if we expect to be able to use that holder. If not alloc a new
* holder.
* For the overflow event it's possible that something will use the in
* event holder before we get the lock so we may need to jump back and
* alloc a new holder, this can't happen for most events...
*/
if (!list_empty(&event->holder.event_list)) {
alloc_holder:
holder = fsnotify_alloc_event_holder();
if (!holder)
return ERR_PTR(-ENOMEM);
}
mutex_lock(&group->notification_mutex);
if (group->q_len >= group->max_events) {
event = q_overflow_event;
/*
* we need to return the overflow event
* which means we need a ref
*/
fsnotify_get_event(event);
return_event = event;
/* sorry, no private data on the overflow event */
priv = NULL;
}
if (!list_empty(list) && merge) {
struct fsnotify_event *tmp;
tmp = merge(list, event);
if (tmp) {
mutex_unlock(&group->notification_mutex);
if (return_event)
fsnotify_put_event(return_event);
if (holder != &event->holder)
fsnotify_destroy_event_holder(holder);
return tmp;
}
}
spin_lock(&event->lock);
if (list_empty(&event->holder.event_list)) {
if (unlikely(holder))
fsnotify_destroy_event_holder(holder);
holder = &event->holder;
} else if (unlikely(!holder)) {
/* between the time we checked above and got the lock the in
* event holder was used, go back and get a new one */
spin_unlock(&event->lock);
mutex_unlock(&group->notification_mutex);
if (return_event) {
fsnotify_put_event(return_event);
return_event = NULL;
}
goto alloc_holder;
}
group->q_len++;
holder->event = event;
fsnotify_get_event(event);
list_add_tail(&holder->event_list, list);
if (priv)
list_add_tail(&priv->event_list, &event->private_data_list);
spin_unlock(&event->lock);
mutex_unlock(&group->notification_mutex);
wake_up(&group->notification_waitq);
kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
return return_event;
}
/*
* Remove and return the first event from the notification list. There is a
* reference held on this event since it was on the list. It is the responsibility
* of the caller to drop this reference.
*/
struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
{
struct fsnotify_event *event;
struct fsnotify_event_holder *holder;
BUG_ON(!mutex_is_locked(&group->notification_mutex));
pr_debug("%s: group=%p\n", __func__, group);
holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
event = holder->event;
spin_lock(&event->lock);
holder->event = NULL;
list_del_init(&holder->event_list);
spin_unlock(&event->lock);
/* event == holder means we are referenced through the in event holder */
if (holder != &event->holder)
fsnotify_destroy_event_holder(holder);
group->q_len--;
return event;
}
/*
* This will not remove the event, that must be done with fsnotify_remove_notify_event()
*/
struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
{
struct fsnotify_event *event;
struct fsnotify_event_holder *holder;
BUG_ON(!mutex_is_locked(&group->notification_mutex));
holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
event = holder->event;
return event;
}
/*
* Called when a group is being torn down to clean up any outstanding
* event notifications.
*/
void fsnotify_flush_notify(struct fsnotify_group *group)
{
struct fsnotify_event *event;
struct fsnotify_event_private_data *priv;
mutex_lock(&group->notification_mutex);
while (!fsnotify_notify_queue_is_empty(group)) {
event = fsnotify_remove_notify_event(group);
/* if they don't implement free_event_priv they better not have attached any */
if (group->ops->free_event_priv) {
spin_lock(&event->lock);
priv = fsnotify_remove_priv_from_event(group, event);
spin_unlock(&event->lock);
if (priv)
group->ops->free_event_priv(priv);
}
fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
}
mutex_unlock(&group->notification_mutex);
}
static void initialize_event(struct fsnotify_event *event)
{
INIT_LIST_HEAD(&event->holder.event_list);
atomic_set(&event->refcnt, 1);
spin_lock_init(&event->lock);
INIT_LIST_HEAD(&event->private_data_list);
}
/*
* Caller damn well better be holding whatever mutex is protecting the
* old_holder->event_list and the new_event must be a clean event which
* cannot be found anywhere else in the kernel.
*/
int fsnotify_replace_event(struct fsnotify_event_holder *old_holder,
struct fsnotify_event *new_event)
{
struct fsnotify_event *old_event = old_holder->event;
struct fsnotify_event_holder *new_holder = &new_event->holder;
enum event_spinlock_class {
SPINLOCK_OLD,
SPINLOCK_NEW,
};
pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, new_event);
/*
* if the new_event's embedded holder is in use someone
* screwed up and didn't give us a clean new event.
*/
BUG_ON(!list_empty(&new_holder->event_list));
spin_lock_nested(&old_event->lock, SPINLOCK_OLD);
spin_lock_nested(&new_event->lock, SPINLOCK_NEW);
new_holder->event = new_event;
list_replace_init(&old_holder->event_list, &new_holder->event_list);
spin_unlock(&new_event->lock);
spin_unlock(&old_event->lock);
/* event == holder means we are referenced through the in event holder */
if (old_holder != &old_event->holder)
fsnotify_destroy_event_holder(old_holder);
fsnotify_get_event(new_event); /* on the list take reference */
fsnotify_put_event(old_event); /* off the list, drop reference */
return 0;
}
struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event)
{
struct fsnotify_event *event;
event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
if (!event)
return NULL;
pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, event);
memcpy(event, old_event, sizeof(*event));
initialize_event(event);
if (event->name_len) {
event->file_name = kstrdup(old_event->file_name, GFP_KERNEL);
if (!event->file_name) {
kmem_cache_free(fsnotify_event_cachep, event);
return NULL;
}
}
event->tgid = get_pid(old_event->tgid);
if (event->data_type == FSNOTIFY_EVENT_PATH)
path_get(&event->path);
return event;
}
/*
* fsnotify_create_event - Allocate a new event which will be sent to each
* group's handle_event function if the group was interested in this
* particular event.
*
* @to_tell the inode which is supposed to receive the event (sometimes a
* parent of the inode to which the event happened.
* @mask what actually happened.
* @data pointer to the object which was actually affected
* @data_type flag indication if the data is a file, path, inode, nothing...
* @name the filename, if available
*/
struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
int data_type, const unsigned char *name,
u32 cookie, gfp_t gfp)
{
struct fsnotify_event *event;
event = kmem_cache_zalloc(fsnotify_event_cachep, gfp);
if (!event)
return NULL;
pr_debug("%s: event=%p to_tell=%p mask=%x data=%p data_type=%d\n",
__func__, event, to_tell, mask, data, data_type);
initialize_event(event);
if (name) {
event->file_name = kstrdup(name, gfp);
if (!event->file_name) {
kmem_cache_free(fsnotify_event_cachep, event);
return NULL;
}
event->name_len = strlen(event->file_name);
}
event->tgid = get_pid(task_tgid(current));
event->sync_cookie = cookie;
event->to_tell = to_tell;
event->data_type = data_type;
switch (data_type) {
case FSNOTIFY_EVENT_PATH: {
struct path *path = data;
event->path.dentry = path->dentry;
event->path.mnt = path->mnt;
path_get(&event->path);
break;
}
case FSNOTIFY_EVENT_INODE:
event->inode = data;
break;
case FSNOTIFY_EVENT_NONE:
event->inode = NULL;
event->path.dentry = NULL;
event->path.mnt = NULL;
break;
default:
BUG();
}
event->mask = mask;
return event;
}
static __init int fsnotify_notification_init(void)
{
fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
q_overflow_event = fsnotify_create_event(NULL, FS_Q_OVERFLOW, NULL,
FSNOTIFY_EVENT_NONE, NULL, 0,
GFP_KERNEL);
if (!q_overflow_event)
panic("unable to allocate fsnotify q_overflow_event\n");
return 0;
}
subsys_initcall(fsnotify_notification_init);