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

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Message-ID: <20120925194017.GK16296@google.com>
Date:	Tue, 25 Sep 2012 12:40:17 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Maxim Levitsky <maximlevitsky@...il.com>
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, Sep 25, 2012 at 09:34:39PM +0200, Maxim Levitsky wrote:
> 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.

Yes the combination of WQ_UNBOUND and max_active==1 guarantees
strictly ordered one-by-one execution.

> 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. 

If you're seeing parallel execution w/ ordered workqueue, it is a
critical bug which would make the kernel crash left and right.  Please
try alloc_ordered_workqueue() and if you still see parallel execution,
please report.

Thanks.

-- 
tejun
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