linux-ext4 - Re: [PATCH v4 15/20] ext4: use ext4_zero_partial_blocks in punch

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Message-ID: <alpine.LFD.2.00.1306201110220.1929@localhost.localdomain>
Date:	Thu, 20 Jun 2013 11:12:02 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
cc:	linux-ext4@...r.kernel.org,
	Ashish Sangwan <ashishsangwan2@...il.com>
Subject: Re: [PATCH v4 15/20] ext4: use ext4_zero_partial_blocks in
 punch_hole

On Wed, 19 Jun 2013, Theodore Ts'o wrote:

> Date: Wed, 19 Jun 2013 19:42:43 -0400
> From: Theodore Ts'o <tytso@....edu>
> To: Lukáš Czerner <lczerner@...hat.com>
> Cc: linux-ext4@...r.kernel.org, Ashish Sangwan <ashishsangwan2@...il.com>
> Subject: Re: [PATCH v4 15/20] ext4: use ext4_zero_partial_blocks in punch_hole
> 
> On Wed, Jun 19, 2013 at 06:37:53PM +0200, Lukáš Czerner wrote:
> > 
> > I think I've got this. The problem actually is in
> > ext4_zero_partial_blocks() where we would attempt to zero out page
> > which has been previously released by truncate_pagecache_range().
> > This might happen when we're punching out just a single page because
> > in ext4_zero_partial_blocks() we do not check whether we're dealing
> > with the whole, or partial page. At the point we're going to zero it
> > out it might have been already released and reused by someone else.
> > 
> > This patch should fix this issue. And indeed with this applied I do
> > not see the problem anymore but I am still testing.
> 
> Thanks for finding this!  I'm still doing testing of your trial patch
> myself, but initial results seem to indicate that this also solves the
> failures 269 and 270 which was apparently uncovered by Ashish's patch
> "ext4: optimize extent selection for block removal in case of hole
> punch".
> 
> 	 		      	    - Ted

Hi Ted,

from my testing I still see problems with test 269, however I've
seen this even without the patch #15 so I am not sure that it's
caused by this.

I'll send a proper patch soon.

Thanks!
-Lukas