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Re: [PATCH] xfs_file_last_byte() needs to acquire ilock

To: Lachlan McIlroy <lmcilroy@xxxxxxxxxx>
Subject: Re: [PATCH] xfs_file_last_byte() needs to acquire ilock
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Fri, 24 Apr 2009 13:52:24 -0400
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1624785772.3251240539480564.JavaMail.root@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
References: <1624785772.3251240539480564.JavaMail.root@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Thu, Apr 23, 2009 at 10:18:00PM -0400, Lachlan McIlroy wrote:
> We had some systems crash with this stack:
> [<a00000010000cb20>] ia64_leave_kernel+0x0/0x280
> [<a00000021291ca00>] xfs_bmbt_get_startoff+0x0/0x20 [xfs]
> [<a0000002129080b0>] xfs_bmap_last_offset+0x210/0x280 [xfs]
> [<a00000021295b010>] xfs_file_last_byte+0x70/0x1a0 [xfs]
> [<a00000021295b200>] xfs_itruncate_start+0xc0/0x1a0 [xfs]
> [<a0000002129935f0>] xfs_inactive_free_eofblocks+0x290/0x460 [xfs]
> [<a000000212998fb0>] xfs_release+0x1b0/0x240 [xfs]
> [<a0000002129ad930>] xfs_file_release+0x70/0xa0 [xfs]
> [<a000000100162ea0>] __fput+0x1a0/0x420
> [<a000000100163160>] fput+0x40/0x60
> The problem here is that xfs_file_last_byte() does not acquire the
> inode lock and can therefore race with another thread that is modifying
> the extext list.  While xfs_bmap_last_offset() is trying to lookup
> what was the last extent some extents were merged and the extent list
> shrunk so the index we lookup is now beyond the end of the extent list
> and potentially in a freed buffer.

Looks good.

Reviewed-by: Christoph Hellwig <hch@xxxxxx>

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