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authorNick Piggin <npiggin@suse.de>2008-02-06 01:37:28 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-06 10:41:06 -0800
commitd599e36a9ea85432587f4550acc113cd7549d12a (patch)
tree2baec196271ccafac682b4bdbef3690cca686221 /fs/inotify.c
parenteea63e0e8a60d00485b47fb6e75d9aa2566b989b (diff)
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>
Diffstat (limited to 'fs/inotify.c')
-rw-r--r--fs/inotify.c13
1 files changed, 10 insertions, 3 deletions
diff --git a/fs/inotify.c b/fs/inotify.c
index 2c5b92152876..b2b109bf29d6 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);