linux-kernel - Re: [PATCH v2] scsi: core: Fix shost->cmd_per_lun calculation in scsi_add_host_with

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Date:   Fri, 8 Oct 2021 11:19:47 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     kys@...rosoft.com, sthemmin@...rosoft.com, wei.liu@...nel.org,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        haiyangz@...rosoft.com, bvanassche@....org, john.garry@...wei.com,
        linux-scsi@...r.kernel.org, linux-hyperv@...r.kernel.org,
        longli@...rosoft.com, mikelley@...rosoft.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] scsi: core: Fix shost->cmd_per_lun calculation in
 scsi_add_host_with_dma()

On Thu, Oct 07, 2021 at 10:49:57AM -0700, Dexuan Cui wrote:
> After commit ea2f0f77538c, a 416-CPU VM running on Hyper-V hangs during
> boot because scsi_add_host_with_dma() sets shost->cmd_per_lun to a
> negative number (the below numbers may differ in different kernel versions):
> in drivers/scsi/storvsc_drv.c, 	storvsc_drv_init() sets
> 'max_outstanding_req_per_channel' to 352, and storvsc_probe() sets
> 'max_sub_channels' to (416 - 1) / 4 = 103 and sets scsi_driver.can_queue to
> 352 * (103 + 1) * (100 - 10) / 100 = 32947, which exceeds SHRT_MAX.
> 
> Use min_t(int, ...) to fix the issue.
> 
> Fixes: ea2f0f77538c ("scsi: core: Cap scsi_host cmd_per_lun at can_queue")
> Cc: stable@...r.kernel.org
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> ---
> 
> v1 tried to fix the issue by changing the storvsc driver:
> https://lwn.net/ml/linux-kernel/BYAPR21MB1270BBC14D5F1AE69FC31A16BFB09@BYAPR21MB1270.namprd21.prod.outlook.com/
> 
> v2 directly fixes the scsi core change instead as Michael Kelley and
> John Garry suggested (refer to the above link).
> 
>  drivers/scsi/hosts.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index 3f6f14f0cafb..24b72ee4246f 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -220,7 +220,8 @@ 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,
> +	/* Use min_t(int, ...) in case shost->can_queue exceeds SHRT_MAX */
> +	shost->cmd_per_lun = min_t(int, shost->cmd_per_lun,
>  				   shost->can_queue);

Looks fine:

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

-- 
Ming