Re: FAILED: patch "[PATCH] block: mq-deadline: Fix dd_finish_request() for zoned devices" failed to apply to 5.15-stable tree

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 1/4/23 23:21, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 5.15-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Greg,

I sent you a backport in reply to your email.

Thanks !

> 
> Possible dependencies:
> 
> 2820e5d0820a ("block: mq-deadline: Fix dd_finish_request() for zoned devices")
> 
> thanks,
> 
> greg k-h
> 
> ------------------ original commit in Linus's tree ------------------
> 
> From 2820e5d0820ac4daedff1272616a53d9c7682fd2 Mon Sep 17 00:00:00 2001
> From: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> Date: Thu, 24 Nov 2022 11:12:07 +0900
> Subject: [PATCH] block: mq-deadline: Fix dd_finish_request() for zoned devices
> 
> dd_finish_request() tests if the per prio fifo_list is not empty to
> determine if request dispatching must be restarted for handling blocked
> write requests to zoned devices with a call to
> blk_mq_sched_mark_restart_hctx(). While simple, this implementation has
> 2 problems:
> 
> 1) Only the priority level of the completed request is considered.
>    However, writes to a zone may be blocked due to other writes to the
>    same zone using a different priority level. While this is unlikely to
>    happen in practice, as writing a zone with different IO priorirites
>    does not make sense, nothing in the code prevents this from
>    happening.
> 2) The use of list_empty() is dangerous as dd_finish_request() does not
>    take dd->lock and may run concurrently with the insert and dispatch
>    code.
> 
> Fix these 2 problems by testing the write fifo list of all priority
> levels using the new helper dd_has_write_work(), and by testing each
> fifo list using list_empty_careful().
> 
> Fixes: c807ab520fc3 ("block/mq-deadline: Add I/O priority support")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> Link: https://lore.kernel.org/r/20221124021208.242541-2-damien.lemoal@opensource.wdc.com
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> 
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index 5639921dfa92..36374481cb87 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -789,6 +789,18 @@ static void dd_prepare_request(struct request *rq)
>  	rq->elv.priv[0] = NULL;
>  }
>  
> +static bool dd_has_write_work(struct blk_mq_hw_ctx *hctx)
> +{
> +	struct deadline_data *dd = hctx->queue->elevator->elevator_data;
> +	enum dd_prio p;
> +
> +	for (p = 0; p <= DD_PRIO_MAX; p++)
> +		if (!list_empty_careful(&dd->per_prio[p].fifo_list[DD_WRITE]))
> +			return true;
> +
> +	return false;
> +}
> +
>  /*
>   * Callback from inside blk_mq_free_request().
>   *
> @@ -828,9 +840,10 @@ static void dd_finish_request(struct request *rq)
>  
>  		spin_lock_irqsave(&dd->zone_lock, flags);
>  		blk_req_zone_write_unlock(rq);
> -		if (!list_empty(&per_prio->fifo_list[DD_WRITE]))
> -			blk_mq_sched_mark_restart_hctx(rq->mq_hctx);
>  		spin_unlock_irqrestore(&dd->zone_lock, flags);
> +
> +		if (dd_has_write_work(rq->mq_hctx))
> +			blk_mq_sched_mark_restart_hctx(rq->mq_hctx);
>  	}
>  }
>  
> 

-- 
Damien Le Moal
Western Digital Research