Re: Race inotify_rm_watch vs umount

[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

On 03/06/2012 04:02 PM, Joseph Salisbury wrote:
> Forwarded conversation
> Subject: *Race inotify_rm_watch vs umount*
> ------------------------
>
> From: *OGAWA Hirofumi* <hirofumi@xxxxxxxxxxxxxxxxxx
> <mailto:hirofumi@xxxxxxxxxxxxxxxxxx>>
> Date: Fri, Jun 10, 2011 at 7:20 AM
> To: John McCutchan <john@xxxxxxxxxxxxxxxxx
> <mailto:john@xxxxxxxxxxxxxxxxx>>, Robert Love <rlove@xxxxxxxxx
> <mailto:rlove@xxxxxxxxx>>, Eric Paris <eparis@xxxxxxxxxx
> <mailto:eparis@xxxxxxxxxx>>
> Cc: linux-kernel@xxxxxxxxxxxxxxx <mailto:linux-kernel@xxxxxxxxxxxxxxx>,
> linux-fsdevel@xxxxxxxxxxxxxxx <mailto:linux-fsdevel@xxxxxxxxxxxxxxx>
>
>
> 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@xxxxxxxxxxxxxxxxxx
> <mailto:hirofumi@xxxxxxxxxxxxxxxxxx>>
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> ----------
> From: *Eric Paris* <eparis@xxxxxxxxxx <mailto:eparis@xxxxxxxxxx>>
> Date: Fri, Jun 10, 2011 at 9:46 AM
> To: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx
> <mailto:hirofumi@xxxxxxxxxxxxxxxxxx>>
> Cc: John McCutchan <john@xxxxxxxxxxxxxxxxx
> <mailto:john@xxxxxxxxxxxxxxxxx>>, Robert Love <rlove@xxxxxxxxx
> <mailto:rlove@xxxxxxxxx>>, linux-kernel@xxxxxxxxxxxxxxx
> <mailto:linux-kernel@xxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx
> <mailto:linux-fsdevel@xxxxxxxxxxxxxxx>
>
>
> 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@xxxxxxxxxxxxxxxxxx <mailto:viro@xxxxxxxxxxxxxxxxxx>>
> Date: Fri, Jun 10, 2011 at 10:35 AM
> To: Eric Paris <eparis@xxxxxxxxxx <mailto:eparis@xxxxxxxxxx>>
> Cc: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx
> <mailto:hirofumi@xxxxxxxxxxxxxxxxxx>>, John McCutchan
> <john@xxxxxxxxxxxxxxxxx <mailto:john@xxxxxxxxxxxxxxxxx>>, Robert Love
> <rlove@xxxxxxxxx <mailto:rlove@xxxxxxxxx>>, linux-kernel@xxxxxxxxxxxxxxx
> <mailto:linux-kernel@xxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx
> <mailto:linux-fsdevel@xxxxxxxxxxxxxxx>
>
>
> 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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