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SubjectRe: Race inotify_rm_watch vs umount
On 03/06/2012 04:02 PM, Joseph Salisbury wrote:
>
>
> Forwarded conversation
> Subject: *Race inotify_rm_watch vs umount*
> ------------------------
>
> From: *OGAWA Hirofumi* <hirofumi@mail.parknet.co.jp
> <mailto:hirofumi@mail.parknet.co.jp>>
> Date: Fri, Jun 10, 2011 at 7:20 AM
> To: John McCutchan <john@johnmccutchan.com
> <mailto:john@johnmccutchan.com>>, Robert Love <rlove@rlove.org
> <mailto:rlove@rlove.org>>, Eric Paris <eparis@redhat.com
> <mailto:eparis@redhat.com>>
> Cc: linux-kernel@vger.kernel.org <mailto:linux-kernel@vger.kernel.org>,
> linux-fsdevel@vger.kernel.org <mailto:linux-fsdevel@vger.kernel.org>
>
>
> 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@mail.parknet.co.jp
> <mailto:hirofumi@mail.parknet.co.jp>>
> --
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>
> ----------
> From: *Eric Paris* <eparis@redhat.com <mailto:eparis@redhat.com>>
> Date: Fri, Jun 10, 2011 at 9:46 AM
> To: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp
> <mailto:hirofumi@mail.parknet.co.jp>>
> Cc: John McCutchan <john@johnmccutchan.com
> <mailto:john@johnmccutchan.com>>, Robert Love <rlove@rlove.org
> <mailto:rlove@rlove.org>>, linux-kernel@vger.kernel.org
> <mailto:linux-kernel@vger.kernel.org>, linux-fsdevel@vger.kernel.org
> <mailto:linux-fsdevel@vger.kernel.org>
>
>
> Ok, I see what you are saying, I'll see what I can do. I'm a little
> scared to call something like iput() under a lock though. I might be
> able to make the bigest lock a mutex and fix this....
>
> I'll add this to my test suite.
>
> -Eric
> >
> > 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.
>
>
> --
>
> ----------
> From: *Al Viro* <viro@zeniv.linux.org.uk <mailto:viro@zeniv.linux.org.uk>>
> Date: Fri, Jun 10, 2011 at 10:35 AM
> To: Eric Paris <eparis@redhat.com <mailto:eparis@redhat.com>>
> Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp
> <mailto:hirofumi@mail.parknet.co.jp>>, John McCutchan
> <john@johnmccutchan.com <mailto:john@johnmccutchan.com>>, Robert Love
> <rlove@rlove.org <mailto:rlove@rlove.org>>, linux-kernel@vger.kernel.org
> <mailto:linux-kernel@vger.kernel.org>, linux-fsdevel@vger.kernel.org
> <mailto:linux-fsdevel@vger.kernel.org>
>
>
> Which lock would that be? I don't see any good candidates in there...
>
>

Hello,

It appears this bug still exists in the 3.2 kernel[0]. There was some
discussion about this bug in this thread and in the bug[1]. However,
there haven't been any updates in a while.

Has there been any further findings on this issue?

Thanks,

Joe


[0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/922906
[1] https://bugzilla.kernel.org/show_bug.cgi?id=22602


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