linux-kernel - Re: [PATCH] xfs: Fix possible truncation of log data in xlog_bread

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Message-ID: <20130304210311.GQ23616@dastard>
Date:	Tue, 5 Mar 2013 08:03:11 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Tony Lu <zlu@...era.com>
Cc:	Mark Tinguely <tinguely@....com>, Alex Elder <elder@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	"xfs@....sgi.com" <xfs@....sgi.com>, Ben Myers <bpm@....com>,
	Dave Chinner <dchinner@...hat.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] xfs: Fix possible truncation of log data in
 xlog_bread_noalign()

On Mon, Mar 04, 2013 at 08:32:45AM +0000, Tony Lu wrote:
> Thanks for you following up.
> 
> My apologize that I just found that it is one change I made before
> that causes this problem. This change forces mkfs.xfs to format
> xfs partitions whose sectorsize were not smaller than 4096 bytes,
> which was due to a bug that earlier versions of xfs used (struct
> *page)->private(long) as a bitmap to represent each block's state
> within a page (the size of a page could be 64K or larger, then it
> needs 128 bit or more to represent each block's state within a
> page).

You do realise that bug doesn't affect x86-64 platforms as they
don't support 64k pages?

> This is reproducible on 2.6.38.6 kernel on X86. But I do not get
> why this change makes the xfs log inconsistent during
> mount/cp/umount operations.

Neither do I, and I don't care to look any further because the
problem is of your own making. In future, please check first that
the bug you are reporting is reproducable on a current upstream
kernel and userspace.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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