linux-kernel - Re: [PATCH] block: blk-mq-sched: Replace GFP_ATOMIC with GFP_KERNEL in blk_mq_sched_assign

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Message-ID: <20180125052937.GA21712@ming.t460p>
Date:   Thu, 25 Jan 2018 13:29:38 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Jia-Ju Bai <baijiaju1990@...il.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: blk-mq-sched: Replace GFP_ATOMIC with GFP_KERNEL
 in blk_mq_sched_assign_ioc

On Wed, Jan 24, 2018 at 08:34:14PM -0700, Jens Axboe wrote:
> On 1/24/18 7:46 PM, Jia-Ju Bai wrote:
> > The function ioc_create_icq here is not called in atomic context.
> > Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
> > 
> > This is found by a static analysis tool named DCNS written by myself.
> 
> But it's running off the IO submission path, so by definition the GFP
> mask cannot include anything that will do IO. GFP_KERNEL will make
> it deadlock prone.
> 
> It could be GFP_NOIO, but that's also overlooking the fact that we can
> have preemption disabled here.

We have REQ_NOWAIT request too, so GFP_NOIO isn't OK too.

-- 
Ming