linux-ext4 - Re: [PATCH 1/2] ext4: fix journal ref count in move_extent_par

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Message-ID: <4A77F014.7060403@rs.jp.nec.com>
Date:	Tue, 04 Aug 2009 17:23:48 +0900
From:	Akira Fujita <a-fujita@...jp.nec.com>
To:	Peng Tao <bergwolf@...il.com>
CC:	linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Subject: Re: [PATCH 1/2] ext4: fix journal ref count in move_extent_par_page

Peng Tao wrote:
> Hi, Akira,
> 
> 2009/8/3 Akira Fujita <a-fujita@...jp.nec.com>:
>> Hi Peng,
>>
>> Peng Tao wrote:
>>> move_extent_par_page calls a_ops->write_begin() to increase journal handler's
>>> reference count. However, if either mext_replace_branches() or ext4_get_block
>>> fails, the increased reference count isn't decreased. This will cause later
>>> umounting of the fs forever hangs. The patch addresses the issue by calling
>>> ext4_journal_stop() if page is not NULL (which means a_ops->write_end() isn't
>>> invoked).
>> In case mext_replaced_branches() or ext4_get_block failed,
>> ext4_journal_stop() is called at out2 label(*)
>> and then journal reference counter is decreased.
>> Therefore I think this fix is not necessary.
> well, the orginal code calls both ext4_journal_start and
> a_ops->write_begin(). So the journal reference was increased twice but
> only gets decreased once in case of failure. This can be simply
> verified by returning -1 at the begining of mext_replaced_branches().
> With such modification, the fs cannot be umounted because of the wrong
> reference count.

Ah, I missed.
Sorry for the noise.
The patch looks good to me.

Regards,
Akira Fujita
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