linux-kernel - Re: Race in wb_do

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Message-ID: <4C2B97D7.60303@athenacr.com>
Date:	Wed, 30 Jun 2010 15:15:35 -0400
From:	Brian Bloniarz <bmb@...enacr.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Larry Woodman <lwoodman@...hat.com>, linux-kernel@...r.kernel.org,
	riel@...hat.com, Mark Lord <kernel@...savvy.com>,
	stefan.bader@...onical.com, kees@...ntu.com
Subject: Re: Race in wb_do_writeback() ???

On 06/29/2010 04:26 PM, Christoph Hellwig wrote:
> On Tue, Jun 29, 2010 at 04:28:16PM -0400, Larry Woodman wrote:
>> Chistoph, I am seeing slabcache corruption.  wb_do_writeback() calls
>> wb_clear_pending() which can queue up the freeing of the bdi_work. Then
>> it calls wb_writeback() which can block, resulting in using the bdi_work
>> after its freed.
>> 
>> ------------------------------------------------------------------
>>   /*
>>    * If this isn't a data integrity operation, just notify
>>    * that we have seen this work and we are now starting it.
>>    */
>>   if (!test_bit(WS_ONSTACK, &work->state))
>>          wb_clear_pending(wb, work);
>> 
>>   wrote += wb_writeback(wb, &args);
>> 
>>  /*
>>   * This is a data integrity writeback, so only do the
>>   * notification when we have completed the work.
>>   */
>>   if (test_bit(WS_ONSTACK, &work->state))
>>          wb_clear_pending(wb, work);
>> ------------------------------------------------------------------
>> 
>> Can you have one unconditional call to wb_clear_pending() after the
>> calling wb_writeback()???
> 
> In fact we should only have a conditional call after wb_writeback.
> I've done that already and it's in Jens' tree for 2.6.36:
> 
>   http://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff;h=79338d2a78ab78efdc1698f1309766a039addf9d

Hi Christoph, 

Is this a problem that was introduced by your writeback patch
series which just got merged for 2.6.35?
Are you going to try to get a fix for this into 2.6.35?

(CCing some people who were interested in your writeback series).
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