On Tue, 2013-04-23 at 08:48 -0500, Mark Tinguely wrote:
> 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@xxxxxxxxxx>
> > 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@xxxxxxxxxx>
> > Reviewed-by: Brian Foster<bfoster@xxxxxxxxxx>
> > Reviewed-by: Ben Myers<bpm@xxxxxxx>
> > Signed-off-by: Ben Myers<bpm@xxxxxxx>
> >
> >> 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.
I second that.
Is there any reason we should _not_ check the return value from
xfs_perag_get() for NULL ?
>
> --Mark.
>
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