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inotify: fix race 

There is a race between setting an inode's children's "parent watched" flag
when placing the first watch on a parent, and instantiating new children of
that parent: a child could miss having its flags set by
set_dentry_child_flags, but then inotify_d_instantiate might still see
!inotify_inode_watched.

The solution is to set_dentry_child_flags after adding the watch.  Locking is
taken care of, because both set_dentry_child_flags and inotify_d_instantiate
hold dcache_lock and child->d_locks.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Robert Love <rlove@google.com>
Cc: John McCutchan <ttb@tentacle.dhs.org>
Cc: Jan Kara <jack@ucw.cz>
Cc: Yan Zheng <yanzheng@21cn.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Piggin 2008-02-06 01:37:28 -08:00 committed by Linus Torvalds
parent eea63e0e8a
commit d599e36a9e
1 changed files with 10 additions and 3 deletions
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13
fs/inotify.c
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@ -627,6 +627,7 @@ s32 inotify_add_watch(struct inotify_handle *ih, struct inotify_watch *watch,
struct inode *inode, u32 mask)
{
int ret = 0;
int newly_watched;
/* don't allow invalid bits: we don't want flags set */
mask &= IN_ALL_EVENTS | IN_ONESHOT;
@ -653,12 +654,18 @@ s32 inotify_add_watch(struct inotify_handle *ih, struct inotify_watch *watch,
*/
watch->inode = igrab(inode);
if (!inotify_inode_watched(inode))
set_dentry_child_flags(inode, 1);
/* Add the watch to the handle's and the inode's list */
newly_watched = !inotify_inode_watched(inode);
list_add(&watch->h_list, &ih->watches);
list_add(&watch->i_list, &inode->inotify_watches);
/*
* Set child flags _after_ adding the watch, so there is no race
* windows where newly instantiated children could miss their parent's
* watched flag.
*/
if (newly_watched)
set_dentry_child_flags(inode, 1);
out:
mutex_unlock(&ih->mutex);
mutex_unlock(&inode->inotify_mutex);