linux-kernel - Re: [PATCH 001 of 2] Fix read/truncate race.

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Message-Id: <20070607231042.97c7b68b.akpm@linux-foundation.org>
Date:	Thu, 7 Jun 2007 23:10:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Neil Brown <neilb@...e.de>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 001 of 2] Fix read/truncate race.

On Fri, 8 Jun 2007 12:48:48 +1000 Neil Brown <neilb@...e.de> wrote:

> The following patch will remove the extra seqlock except when we
> actually need it and remove the extra arithmetic - but I haven't
> tested it or reviewed it properly.  I can do that if you think it is
> the right direction.

Yes, the optimisation is valid and looks useful.

>  ./mm/filemap.c |   34 ++++++++++++++++++++++++++++------

It didn't apply - your tree seems different from mine.

> +		 *
> +		 * NOTE: This access of inode->i_size is not protected
> +		 *  and if there is a concurrent update on a 32bit machine,
> +		 *  it could return the wrong value.  This could only be a problem
> +		 *  if i_size has actually changed to a smaller value before the
> +		 *  page became uptodate, and at this point it still has a smaller
> +		 *  value, but due to a race while reading, it appears unchanged.
> +		 *  The chances of this happening are so small and the consequence
> +		 *  sufficiently minor, that the cost of the seqlock seems
> +		 *  not to be justified.

please consider incorporating scripts/checkpatch.pl into your patch
preparation toolchain.

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