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Date:   Mon, 29 Aug 2022 10:13:58 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     ZiyangZhang <ZiyangZhang@linux.alibaba.com>
Cc:     axboe@kernel.dk, xiaoguang.wang@linux.alibaba.com,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        joseph.qi@linux.alibaba.com
Subject: Re: [RFC PATCH 1/9] ublk_drv: check 'current' instead of 'ubq_daemon'
Message-ID: <Ywwg5hCZSh0QQfYF@T590>
References: <20220824054744.77812-1-ZiyangZhang@linux.alibaba.com>
 <20220824054744.77812-2-ZiyangZhang@linux.alibaba.com>
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In-Reply-To: <20220824054744.77812-2-ZiyangZhang@linux.alibaba.com>
Precedence: bulk

On Wed, Aug 24, 2022 at 01:47:36PM +0800, ZiyangZhang wrote:
> This check is not atomic. So with recovery feature, ubq_daemon may be
> updated simultaneously by recovery task. Instead, check 'current' is
> safe here because 'current' never changes.
> 
> Also add comment explaining this check, which is really important for
> understanding recovery feature.
> 
> Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>
> ---
>  drivers/block/ublk_drv.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 6a4a94b4cdf4..c39b67d7133d 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -645,14 +645,22 @@ static inline void __ublk_rq_task_work(struct request *req)
>  	struct ublk_device *ub = ubq->dev;
>  	int tag = req->tag;
>  	struct ublk_io *io = &ubq->ios[tag];
> -	bool task_exiting = current != ubq->ubq_daemon || ubq_daemon_is_dying(ubq);
>  	unsigned int mapped_bytes;
>  
>  	pr_devel("%s: complete: op %d, qid %d tag %d io_flags %x addr %llx\n",
>  			__func__, io->cmd->cmd_op, ubq->q_id, req->tag, io->flags,
>  			ublk_get_iod(ubq, req->tag)->addr);
>  
> -	if (unlikely(task_exiting)) {
> +	/*
> +	 * Task is exiting if either:
> +	 *
> +	 * (1) current != ubq_daemon.
> +	 * io_uring_cmd_complete_in_task() tries to run task_work
> +	 * in a workqueue if ubq_daemon(cmd's task) is PF_EXITING.
> +	 *
> +	 * (2) current->flags & PF_EXITING.
> +	 */
> +	if (unlikely(current != ubq->ubq_daemon || current->flags & PF_EXITING)) {

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks,
Ming