Messages in this thread Patch in this message | | | Date | Wed, 16 Apr 2008 18:01:31 -0700 | From | Chris Wright <> | Subject | inotify: fix race |
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-stable review patch. If anyone has any objections, please let us know. ---------------------
From: Nick Piggin <npiggin@suse.de>
upstream commit: d599e36a9ea85432587f4550acc113cd7549d12a
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> Cc: Christian Lamparter <chunkeey@web.de> Signed-off-by: Chris Wright <chrisw@sous-sol.org> --- fs/inotify.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
--- a/fs/inotify.c +++ b/fs/inotify.c @@ -627,6 +627,7 @@ s32 inotify_add_watch(struct inotify_han 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_han */ 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); --
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