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Re: [PATCH] xfs: shutdown filesystem if xfs_perag_get fails

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: shutdown filesystem if xfs_perag_get fails
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Tue, 23 Apr 2013 08:48:01 -0500
Cc: Eric Sandeen <sandeen@xxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130422233033.GK30622@dastard>
References: <20130419204102.736961610@xxxxxxx> <20130421174107.007313126@xxxxxxx> <5174603A.8030208@xxxxxxxxxxx> <51753EDE.6000301@xxxxxxx> <51754A13.5000808@xxxxxxxxxxx> <5175532B.3050509@xxxxxxx> <20130422233033.GK30622@dastard>
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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...



Thank-you, that make sense.

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


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