linux-kernel - Re: [PATCH v2 memstick: support for legacy sony memsticks

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Date:	Tue, 25 Sep 2012 21:34:39 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alex Dubov <oakad@...oo.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 memstick: support for legacy sony memsticks

On Tue, 2012-09-25 at 11:02 -0700, Tejun Heo wrote: 
> Hello,
> 
> > * Swithced to using a workqueue.
> >   Unfortunelly, I still see that workqueue items are executed in parallel
> >   I suspect that this happens if one work item sleeps. In this case I
> >   don't want other work items to run too. I fixed this with a mutex, and anyway
> >   it nice to have it to guaranteee this.
> 
> You can use alloc_ordered_workqueue("namefmt", WQ_MEM_RECLAIM).  No
> mutex needed for inter-work exclusion.
But this just adds the WQ_UNBOUND. Dunno, without lock I had several
crashes, that for high level of confidence caused by by parallel
execution of work items. Once I added this mutex, I couldnt reproduce
these.

I had the __blk_end_request fail with NULL msb->req. I can't see how
that can happen if work queue isn't executed in parallel.
(and then the I didn't even had by mistake the code that sets it to NULL
in msb_stop, so I really fail to see how that could happen due internal
bug in my code. 
> 
> Thanks.
> 

-- 
Best regards,
        Maxim Levitsky


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