linux-kernel - Re: [PATCH] block: Don't access request after it might be freed

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Message-ID: <50ADFEC2.8040100@kernel.dk>
Date:	Thu, 22 Nov 2012 11:30:26 +0100
From:	Jens Axboe <axboe@...nel.dk>
To:	Roland Dreier <roland@...nel.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: Don't access request after it might be freed

On 2012-11-22 11:00, Roland Dreier wrote:
> From: Roland Dreier <roland@...estorage.com>
> 
> After we've done __elv_add_request() and __blk_run_queue() in
> blk_execute_rq_nowait(), the request might finish and be freed
> immediately.  Therefore checking if the type is REQ_TYPE_PM_RESUME
> isn't safe afterwards, because if it isn't, rq might be gone.
> Instead, check beforehand and stash the result in a temporary.
> 
> This fixes crashes in blk_execute_rq_nowait() I get occasionally when
> running with lots of memory debugging options enabled -- I think this
> race is usually harmless because the window for rq to be reallocated
> is so small.

Thanks Roland, that's obviously a bug, not safe to touch the request
even after insertion, let alone running the queue. Applied.

-- 
Jens Axboe

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