linux-ext4 - Re: [PATCH 4/4] jbd2: don't dirty original metadata buffer on abort

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Message-ID: <20081013203641.GA6469@mail.oracle.com>
Date:	Mon, 13 Oct 2008 13:36:42 -0700
From:	Joel Becker <Joel.Becker@...cle.com>
To:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
Cc:	tytso@....edu, adilger@....com, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	jack@...e.cz
Subject: Re: [PATCH 4/4] jbd2: don't dirty original metadata buffer on abort

On Fri, Oct 10, 2008 at 06:02:09PM +0900, Hidehiro Kawai wrote:
> Currently, original metadata buffers are dirtied when they are
> unfiled whether the journal has aborted or not.  Eventually these
> buffers will be written-back to the filesystem by pdflush.  This
> means some metadata buffers are written to the filesystem without
> journaling if the journal aborts.  So if both journal abort and
> system crash happen at the same time, the filesystem would become
> inconsistent state.  Additionally, replaying journaled metadata
> can overwrite the latest metadata on the filesystem partly.
> Because, if the journal gets aborted, journaled metadata are
> preserved and replayed during the next mount not to lose
> uncheckpointed metadata.  This would also break the consistency
> of the filesystem.
> 
> This patch prevents original metadata buffers from being dirtied
> on abort by clearing BH_JBDDirty flag from those buffers.  Thus,
> no metadata buffers are written to the filesystem without journaling.

	It's not my place to Ack such patches, but I noticed this bug
during Plumbers, and Eric and Andreas pointed me to this patch, which
fixes it quite nicely.  Just $0.02 :-)

Joel

-- 

Life's Little Instruction Book #94

	"Make it a habit to do nice things for people who 
	 will never find out."

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@...cle.com
Phone: (650) 506-8127
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