From: Nick Piggin Date: Wed, 6 Feb 2008 09:37:28 +0000 (-0800) Subject: inotify: fix race X-Git-Tag: v2.6.25-rc1~702 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=d599e36a9ea85432587f4550acc113cd7549d12a;p=linux-2.6-omap-h63xx.git 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 Cc: Robert Love Cc: John McCutchan Cc: Jan Kara Cc: Yan Zheng Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/inotify.c b/fs/inotify.c index 2c5b9215287..b2b109bf29d 100644 --- a/fs/inotify.c +++ b/fs/inotify.c @@ -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);