linux-kernel - Re: [PATCH next/mmotm] ext4: fix cache_es after merge

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Message-ID: <20120927203920.GB9585@thunk.org>
Date:	Thu, 27 Sep 2012 16:39:20 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Zheng Liu <wenqing.lz@...bao.com>,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	Allison Henderson <achender@...ux.vnet.ibm.com>,
	Lukas Czerner <lczerner@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH next/mmotm] ext4: fix cache_es after merge_left

On Thu, Sep 27, 2012 at 01:31:28PM -0700, Hugh Dickins wrote:
> Kernel build with CONFIG_DEBUG_SLAB or CONFIG_SLUB_DEBUG slub_debug=FPZ
> gives me kernel BUG at fs/ext4/extents_status.c:142!  That's the
> BUG_ON(es->start + es->len < es->start) in extent_status_end() called
> from ext4_es_insert_extent().  tree->cache_es has been freed and poisoned.
> 
> This comes from when ext4_es_try_to_merge_left() merges es into leftward
> es1, but ext4_es_insert_extent()'s out then updates cache_es to the freed
> extent_status.  ext4_es_try_to_merge_right() does not pose a problem.
> 
> Change ext4_es_try_to_merge_left() to return whichever extent_status
> should be recorded in tree->cache_es.  Remove cache_es update from
> both of them, leaving that to ext4_es_insert_extent()'s out label.
> 
> Signed-off-by: Hugh Dickins <hughd@...gle.com>

Hugh, thanks for finding this bug!

Zheng, you were going to send me an updated patch series; can you take
care of merging this patch into your patch series (and crediting Hugh
with a Signed-off-by as appropriate)?

Thanks!!

					- Ted
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