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Date: Wed, 28 Aug 2013 15:31:09 -0500
From: Mark Tinguely <tinguely@sgi.com>
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Subject: Re: [PATCH 1/2] xfs: btree block LSN escaping to disk uninitialised
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To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com

On 08/28/13 06:22, Dave Chinner wrote:
> From: Dave Chinner<dchinner@redhat.com>
>
> When testing LSN ordering code for v5 superblocks, it was discovered
> that the the LSN embedded in the generic btree blocks was
> occasionally uninitialised. These values didn't get written to disk
> by metadata writeback - they got written by previous transactions in
> log recovery.
>
> The issue is here that the when the block is first allocated and
> initialised, the LSN field was not initialised - it gets overwritten
> before IO is issued on the buffer - but the value that is logged by
> transactions that modify the header before it is written to disk
> (and initialised) contain garbage. Hence the first recovery of the
> buffer will stamp garbage into the LSN field, and that can cause
> subsequent transactions to not replay correctly.
>
> The fix is simply to initialise the bb_lsn field to zero when we
> initialise the block for the first time.
>
> Signed-off-by: Dave Chinner<dchinner@redhat.com>
> ---


This is simple enough that it could have been put into the second patch.

Reviewed-by: Mark Tinguely <tinguely@sgi.com>

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