linux-kernel - Race inotify_rm

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Message-ID: <87r572nd9k.fsf@devron.myhome.or.jp>
Date:	Fri, 10 Jun 2011 20:20:55 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	John McCutchan <john@...nmccutchan.com>,
	Robert Love <rlove@...ve.org>, Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Race inotify_rm_watch vs umount

Hi,

I'm looking the race inotify_rm_watch() vs umount(). This race become the
cause of Oops. You can see the oops at

https://bugzilla.kernel.org/show_bug.cgi?id=22602

So, what race?

umount                               inotify_rm_watch
  ...                                  fsnotify_destroy_mark()
                                         fsnotify_destroy_inode_mark()
                                           /* removed from i_fsnotify_marks */
    generic_shutdown_super()
      fsnotify_unmount_inodes()
        put_super()
                                           iput()
                                             iput_final()
                                               /* this is after put_super() */

Like above, inotify doesn't guarantee to call final iput() before
put_super(). With this violation, FS driver can oops.

Well, so, what are requested for inotify?  We can't simply take
sb->s_umount in inotify_rm_watch()?

Any ideas?

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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