linux-kernel - Re: [PATCH -next 1/2] block, bfq: protect 'bfqd->queued' by 'bfqd->lock'

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Message-ID: <20220511135227.lawvrlrajtyszwfb@quack3.lan>
Date:   Wed, 11 May 2022 15:52:27 +0200
From:   Jan Kara <jack@...e.cz>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     jack@...e.cz, paolo.valente@...aro.org, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH -next 1/2] block, bfq: protect 'bfqd->queued' by
 'bfqd->lock'

On Tue 10-05-22 21:16:28, Yu Kuai wrote:
> If bfq_schedule_dispatch() is called from bfq_idle_slice_timer_body(),
> then 'bfqd->queued' is read without holding 'bfqd->lock'. This is
> wrong since it can be wrote concurrently.
> 
> Fix the problem by holding 'bfqd->lock' for bfq_schedule_dispatch(),
> like everywhere else.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  block/bfq-iosched.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 272d48d8f326..61750696e87f 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -456,6 +456,8 @@ static struct bfq_io_cq *bfq_bic_lookup(struct request_queue *q)
>   */
>  void bfq_schedule_dispatch(struct bfq_data *bfqd)
>  {
> +	lockdep_assert_held(&bfqd->lock);
> +
>  	if (bfqd->queued != 0) {
>  		bfq_log(bfqd, "schedule dispatch");
>  		blk_mq_run_hw_queues(bfqd->queue, true);
> @@ -6898,8 +6900,8 @@ bfq_idle_slice_timer_body(struct bfq_data *bfqd, struct bfq_queue *bfqq)
>  	bfq_bfqq_expire(bfqd, bfqq, true, reason);
>  
>  schedule_dispatch:
> -	spin_unlock_irqrestore(&bfqd->lock, flags);
>  	bfq_schedule_dispatch(bfqd);
> +	spin_unlock_irqrestore(&bfqd->lock, flags);
>  }
>  
>  /*
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR