Re: [PATCH] scsi: Update max_hw_sectors on rescan

From: John Garry <john.g.garry@oracle.com>
To: Brian King <brking@linux.vnet.ibm.com>, linux-scsi@vger.kernel.org
Cc: brking@pobox.com, jejb@linux.ibm.com, martin.petersen@oracle.com
Subject: Re: [PATCH] scsi: Update max_hw_sectors on rescan
Date: Thu, 18 Jan 2024 15:44:47 +0000	[thread overview]
Message-ID: <5326306f-9515-4153-9ef2-e978e775a27f@oracle.com> (raw)
In-Reply-To: <20240117213620.132880-1-brking@linux.vnet.ibm.com>

On 17/01/2024 21:36, Brian King wrote:
> This addresses an issue discovered on ibmvfc LUNs. For this driver,
> max_sectors is negotiated with the VIOS. This gets done at initialization
> time, then LUNs get scanned and things generally work fine. However,
> this attribute can be changed on the VIOS, either due to a sysadmin
> change or potentially a VIOS code level change. If this decreases
> to a smaller value, due to one of these reasons, the next time the
> ibmvfc driver performs an NPIV login, it will only be able to use
> the smaller value. In the case of a VIOS reboot, when the VIOS goes
> down, all paths through that VIOS will go to devloss state. When
> the VIOS comes back up, ibmvfc negotiates max_sectors and will only
> be able to get the smaller value and it will update shost->max_sectors.

Are you saying that the driver will manually update shost->max_sectors 
after adding the scsi host? I didn't think that was permitted.

Thanks,
John

> However, when LUNs are scanned, the devloss paths will be found
> and brought back online, still using the old max_hw_sectors. This
> change ensures that max_hw_sectors gets updated.
> 
> Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
> ---
>   drivers/scsi/scsi_scan.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index 44680f65ea14..01f2b38daab3 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -1162,6 +1162,7 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
>   	blist_flags_t bflags;
>   	int res = SCSI_SCAN_NO_RESPONSE, result_len = 256;
>   	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
> +	struct request_queue *q;
>   
>   	/*
>   	 * The rescan flag is used as an optimization, the first scan of a
> @@ -1182,6 +1183,10 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
>   				*bflagsp = scsi_get_device_flags(sdev,
>   								 sdev->vendor,
>   								 sdev->model);
> +			q = sdev->request_queue;
> +			if (queue_max_hw_sectors(q) > shost->max_sectors)
> +				blk_queue_max_hw_sectors(q, shost->max_sectors);
> +
>   			return SCSI_SCAN_LUN_PRESENT;
>   		}
>   		scsi_device_put(sdev);
> @@ -2006,4 +2011,3 @@ void scsi_forget_host(struct Scsi_Host *shost)
>   	}
>   	spin_unlock_irqrestore(shost->host_lock, flags);
>   }
> -