[PATCH] xfs: shutdown filesystem if xfs_perag_get fails

[Mark Tinguely]

On 04/22/13 18:30, Dave Chinner wrote:
> On Mon, Apr 22, 2013 at 10:11:39AM -0500, Mark Tinguely wrote:
>>   #6 [ffff880135603980] _xfs_buf_find at ffffffffa01a7fef [xfs]
>>   #7 [ffff8801356039f0] xfs_buf_get at ffffffffa01a824a [xfs]
>>   #8 [ffff880135603a30] xfs_buf_read at ffffffffa01a83a4 [xfs]
>>   #9 [ffff880135603a60] xlog_recover_inode_pass2 at ffffffffa0193629 [xfs]
>
> So it's the same problem as this bug fix addresses:
>
> commit 10616b806d1d7835b1d23b8d75ef638f92cb98b6
> Author: Dave Chinner<dchinner at redhat.com>
> Date:   Mon Jan 21 23:53:52 2013 +1100
>
>      xfs: fix _xfs_buf_find oops on blocks beyond the filesystem end
>
>      When _xfs_buf_find is passed an out of range address, it will fail
>      to find a relevant struct xfs_perag and oops with a null
>      dereference. This can happen when trying to walk a filesystem with a
>      metadata inode that has a partially corrupted extent map (i.e. the
>      block number returned is corrupt, but is otherwise intact) and we
>      try to read from the corrupted block address.
>
>      In this case, just fail the lookup. If it is readahead being issued,
>      it will simply not be done, but if it is real read that fails we
>      will get an error being reported.  Ideally this case should result
>      in an EFSCORRUPTED error being reported, but we cannot return an
>      error through xfs_buf_read() or xfs_buf_get() so this lookup failure
>      may result in ENOMEM or EIO errors being reported instead.
>
>      Signed-off-by: Dave Chinner<dchinner at redhat.com>
>      Reviewed-by: Brian Foster<bfoster at redhat.com>
>      Reviewed-by: Ben Myers<bpm at sgi.com>
>      Signed-off-by: Ben Myers<bpm at sgi.com>
>
>> The recovery value is bad and is a problem on its own, but XFS does
>> not verify the validity of ag number when doing a xfs_perag_get().
>
> Right, that's what the above fix does, but it can't be done on older
> kernels because grwofs relies on being able to get buffers beyond
> the existing filesystem limits...
>
> Cheers,
>
> Dave.

Thank-you, that make sense.

I still do not like assuming xfs_perag_get() will always return a valid 
perag pointer.

--Mark.