linux-kernel - Re: [PATCH] scsi: core: Cap shost cmd_per_lun at can

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Date:   Thu, 20 May 2021 09:24:25 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: core: Cap shost cmd_per_lun at can_queue

On Wed, May 19, 2021 at 10:31:02PM +0800, John Garry wrote:
> Function sdev_store_queue_depth() enforces that the sdev queue depth cannot
> exceed Shost.can_queue.
> 
> The sdev initial value comes from shost cmd_per_lun.
> 
> However, the LLDD may still set cmd_per_lun > can_queue, which leads to an
> initial sdev queue depth greater than can_queue.
> 
> Such an issue was reported in [0], which caused a hang. That has since
> been fixed in commit fc09acb7de31 ("scsi: scsi_debug: Fix cmd_per_lun,
> set to max_queue").
> 
> Stop this possibly happening for other drivers by capping
> shost.cmd_per_lun at shost.can_queue.
> 
> [0] https://lore.kernel.org/linux-scsi/YHaez6iN2HHYxYOh@T590/
> 
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
> Earlier patch was in https://lore.kernel.org/linux-scsi/1618848384-204144-1-git-send-email-john.garry@huawei.com/
> 
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index ba72bd4202a2..624e2582c3df 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -220,6 +220,9 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
>  		goto fail;
>  	}
>  
> +	shost->cmd_per_lun = min_t(short, shost->cmd_per_lun,
> +				   shost->can_queue);
> +
>  	error = scsi_init_sense_cache(shost);
>  	if (error)
>  		goto fail;
> -- 
> 2.26.2
> 

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

-- 
Ming