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

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Date:	Mon, 02 Dec 2013 14:14:45 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Ming Lei <tom.leiming@...il.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] block: fix mq request allocation

Jens Axboe <axboe@...nel.dk> writes:

> 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.

Hmm, did I make it sound as though I thought it wasn't a bug?  Your
response leaves me wondering whether my patch made it to your inbox.

>> p.s. Jens, every time I see GFP_ATOMIC|__GFP_WAIT, my head explodes.  Just sayin'.
>
> It's perfectly fine :-)

Sure, it's not *your* head!  ;-)

-Jeff
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