linux-kernel - Re: [PATCH] blk-mq: move cancel of hctx->run_work to the front of blk_exit

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Date:   Fri, 9 Oct 2020 17:46:40 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Yang Yang <yang.yang@...o.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Bart Van Assche <bvanassche@....org>,
        Hannes Reinecke <hare@...e.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, onlyfever@...oud.com
Subject: Re: [PATCH] blk-mq: move cancel of hctx->run_work to the front of
 blk_exit_queue

On Fri, Oct 09, 2020 at 01:00:14AM -0700, Yang Yang wrote:
> blk_exit_queue will free elevator_data, while blk_mq_run_work_fn
> will access it. Move cancel of hctx->run_work to the front of
> blk_exit_queue to avoid use-after-free.
> 
> Fixes: 1b97871b501f ("blk-mq: move cancel of hctx->run_work into blk_mq_hw_sysfs_release")
> Signed-off-by: Yang Yang <yang.yang@...o.com>
> ---
>  block/blk-mq-sysfs.c | 2 --
>  block/blk-sysfs.c    | 9 ++++++++-
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index 062229395a50..7b52e7657b2d 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/block/blk-mq-sysfs.c
> @@ -36,8 +36,6 @@ static void blk_mq_hw_sysfs_release(struct kobject *kobj)
>  	struct blk_mq_hw_ctx *hctx = container_of(kobj, struct blk_mq_hw_ctx,
>  						  kobj);
>  
> -	cancel_delayed_work_sync(&hctx->run_work);
> -
>  	if (hctx->flags & BLK_MQ_F_BLOCKING)
>  		cleanup_srcu_struct(hctx->srcu);
>  	blk_free_flush_queue(hctx->fq);
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 7dda709f3ccb..8c6bafc801dd 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -934,9 +934,16 @@ static void blk_release_queue(struct kobject *kobj)
>  
>  	blk_free_queue_stats(q->stats);
>  
> -	if (queue_is_mq(q))
> +	if (queue_is_mq(q)) {
> +		struct blk_mq_hw_ctx *hctx;
> +		int i;
> +
>  		cancel_delayed_work_sync(&q->requeue_work);
>  
> +		queue_for_each_hw_ctx(q, hctx, i)
> +			cancel_delayed_work_sync(&hctx->run_work);
> +	}
> +

Looks fine:

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

Thanks,
Ming