linux-kernel - Re: [PATCH] blk-mq: move bio merge attempt to blk_mq_submit

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Message-ID: <330468da-a778-6cfc-ce46-a62566d71c8d@kernel.dk>
Date:   Fri, 12 Aug 2022 06:40:32 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-mq: move bio merge attempt to blk_mq_submit_bio()

On 8/12/22 2:39 AM, Chengming Zhou wrote:
> We will try to get request from cache before alloc request, in
> both cases will first attempt bio merge.
> 
> This patch move this common part to blk_mq_submit_bio(), which
> simplify the code and avoid passing in the pointer of bio.

I don't think this will work. If we get a cached request, then we
know we have a reference to the queue. If you swap these around,
then that's no longer the case and we can have a use-after-free if
the queue goes away.

-- 
Jens Axboe