linux-kernel - Re: [PATCH] block: fix mq request allocation

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Message-ID: <529CBA0A.8020703@kernel.dk>
Date:	Mon, 02 Dec 2013 09:49:14 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Jeff Moyer <jmoyer@...hat.com>, Ming Lei <tom.leiming@...il.com>
CC:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] block: fix mq request allocation

On 12/02/2013 08:20 AM, Jeff Moyer wrote:
> Ming Lei <tom.leiming@...il.com> writes:
> 
>> blk_mq_alloc_request_pinned() may return NULL request in case of
>> !__GFP_WAIT, so cause its callers to derefence NULL pointer for
>> releasing current context.
>>
>> This patch introduces two flags to address the issue.
> 
> Hi, Ming,
> 
> 
> Good catch, but your patch seems overly complicated.  How about
> something like the following (compile-tested only), instead?  Note that
> I did not touch blk_make_request, as the put_ctx there seems to
> correlate to a get_ctx earlier in the function (not a leaked reference
> from __blk_mq_alloc_request).

I would tend to agree, it's overly complicated. The bug is real, however.

> p.s. Jens, every time I see GFP_ATOMIC|__GFP_WAIT, my head explodes.  Just sayin'.

It's perfectly fine :-)

-- 
Jens Axboe

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