linux-kernel - Re: [PATCH] block: put the reference of the io scheduler module after switching back

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Message-ID: <a0d0c50e-061b-ce4e-0341-35156dde00c7@huaweicloud.com>
Date:   Tue, 11 Oct 2022 20:54:13 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Jinlong Chen <chenjinlong2016@...look.com>, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] block: put the reference of the io scheduler module after
 switching back

Hi!

在 2022/10/11 18:21, Jinlong Chen 写道:
> We got a reference of the io scheduler module in
> blk_mq_elv_switch_none to prevent the module from
> being removed. We need to put that reference back
> once we are done.

However, if blk_mq_elv_switch_none() failed due to OOM, and module
reference is not acquired, blk_mq_elv_switch_back() will still be
called. This seems not to be the right fix.

Thanks,
Kuai
> 
> Signed-off-by: Jinlong Chen <chenjinlong2016@...look.com>
> ---
>   block/blk-mq.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 8070b6c10e8d..8dfe3bf3e599 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -4595,6 +4595,13 @@ static void blk_mq_elv_switch_back(struct list_head *head,
>   
>   	mutex_lock(&q->sysfs_lock);
>   	elevator_switch(q, t);
> +	/**
> +	 * We got a reference of the io scheduler module in
> +	 * blk_mq_elv_switch_none to prevent the module from
> +	 * being removed. We need to put that reference back
> +	 * once we are done.
> +	 */
> +	module_put(t->elevator_owner);
>   	mutex_unlock(&q->sysfs_lock);
>   }
>   
>