> On Thu, 23 Aug 2007 11:25:18 -0400 Chuck Ebbert <[email protected]> wrote:
> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=248355
>
> Description of problem:
> Warnings in the kernel log (dmesg):
> BUG: warning at fs/inotify.c:172/set_dentry_child_flags() (Not tainted)
> [<c0497a37>] set_dentry_child_flags+0x67/0x13d
> [<c0497c27>] remove_watch_no_event+0x2f/0x3b
> [<c0497d15>] inotify_remove_watch_locked+0x12/0x3e
> [<c0600c17>] mutex_lock+0x1a/0x29
> [<c0497fdd>] inotify_rm_wd+0x6d/0x8a
> [<c04983b1>] sys_inotify_rm_watch+0x38/0x4f
> [<c0404f70>] syscall_call+0x7/0xb
>
> Appears randomly, about every second/third day.
>
> Still happening in kernel 2.6.22.
>
>
> static void set_dentry_child_flags(struct inode *inode, int watched)
> ...
> spin_lock(&dcache_lock);
> list_for_each_entry(alias, &inode->i_dentry, d_alias) {
> struct dentry *child;
>
> list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {
> if (!child->d_inode) {
> WARN_ON(child->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);
> continue;
> }
>
> But in dcache.c, the locks are dropped before this flag is cleared, leaving
> a race window:
>
> void d_delete(struct dentry * dentry)
> ...
> spin_lock(&dcache_lock);
> spin_lock(&dentry->d_lock);
> isdir = S_ISDIR(dentry->d_inode->i_mode);
> if (atomic_read(&dentry->d_count) == 1) {
> dentry_iput(dentry); <================ drops dcache_lock and dentry->d_lock
> fsnotify_nameremove(dentry, isdir);
>
> /* remove this and other inotify debug checks after 2.6.18 */
> dentry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;
> return;
> }
>
> (The comment is nice, it says the debug code should have been removed long ago.)
We've been chasing this bug for a year or so. Thanks for maybe-solving it.
I forwarded your email to Nick a few days ago but he's presently tied up
with kernel slummit. Please let us not forget about this?
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