Commit:     d599e36a9ea85432587f4550acc113cd7549d12a
Parent:     eea63e0e8a60d00485b47fb6e75d9aa2566b989b
Author:     Nick Piggin <[EMAIL PROTECTED]>
AuthorDate: Wed Feb 6 01:37:28 2008 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Wed Feb 6 10:41:06 2008 -0800

    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
    The solution is to set_dentry_child_flags after adding the watch.  Locking 
    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 <[EMAIL PROTECTED]>
    Cc: Robert Love <[EMAIL PROTECTED]>
    Cc: John McCutchan <[EMAIL PROTECTED]>
    Cc: Jan Kara <[EMAIL PROTECTED]>
    Cc: Yan Zheng <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
 fs/inotify.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/inotify.c b/fs/inotify.c
index 2c5b921..b2b109b 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);
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