linux-kernel - Re: [PATCH] scsi: storvsc: Cap scsi_driver.can

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Date:   Wed, 6 Oct 2021 09:17:57 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
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, ming.lei@...hat.com, bvanassche@....org,
        john.garry@...wei.com, linux-scsi@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] scsi: storvsc: Cap scsi_driver.can_queue to fix a hang
 issue during boot

On Wed, Oct 06, 2021 at 12:03:45AM -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:
> 	'max_outstanding_req_per_channel' is 352,
> 	'max_sub_channels' is (416 - 1) / 4 = 103, so in storvsc_probe(),
> scsi_driver.can_queue = 352 * (103 + 1) * (100 - 10) / 100 = 32947, which
> is bigger than SHRT_MAX (i.e. 32767).
> 
> Fix the hang issue by capping scsi_driver.can_queue.
> 
> Add the below Fixed tag though ea2f0f77538c itself is good.
> 
> 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>
> ---
>  drivers/scsi/storvsc_drv.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index ebbbc1299c62..ba374908aec2 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -1976,6 +1976,16 @@ static int storvsc_probe(struct hv_device *device,
>  				(max_sub_channels + 1) *
>  				(100 - ring_avail_percent_lowater) / 100;
>  
> +	/*
> +	 * v5.14 (see commit ea2f0f77538c) implicitly requires that

No need to put a version number in a comment, they do not track well
when people backport changes all over the place in other kernel trees.

If you want to refer to a commit, please do so in the documented way.

For this case, that would be:
	ea2f0f77538c ("scsi: core: Cap scsi_host cmd_per_lun at can_queue")

thanks,

greg k-h