linux-ext4 - Re: [PATCH] fix for consistency errors after crash

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Message-ID: <20100712193726.GB12804@atrey.karlin.mff.cuni.cz>
Date:	Mon, 12 Jul 2010 21:37:27 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Amir G." <amir73il@...rs.sourceforge.net>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] fix for consistency errors after crash

  Hi,

> I've seen you guys had some open RH bugs on ext3, who all share in
> common the "bit already free" error.
> 
> This bug I reported can explain many different problems in ext[34].
> 
> Essentially, every time there is a kernel crash (or hard reboot)
> during delete/truncate of a large file,
> it may result in "bit already clear" error after reboot.
> 
> The problem is very simple and so is the fix.
> I proved the problem with 100% recreation chances using a small patch,
> instead of running statistical stress tests.
> All I did was to add a print and 10 seconds delay after transaction
> restart in ext3_free_branches and reboot > 5 seconds after the
> transaction restarts, so that kjournald will have time to commit the
> old transaction.
> After the reboot, I always get "bit already clear" errors, because the
> "half large truncate" transaction is not handled properly.
> 
> I did not get any response from ext4 guys so far and since this bug
> dates back to ext3,
> I was hoping you guys could take a look and put your weight on pushing
> the fix upstream.
  Thanks for a ping. Your analysis and the fix looks correct to me. Attached is
a fix of the problem for ext3 which I'll merge if noone objects. BTW: I've also
updated a comment a bit so you might want to include than in an ext4 patch as
well.

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs

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