linux-kernel - RE: [PATCH -next] scsi: storvsc: Fix unsigned comparison to zero

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Message-ID: <MWHPR21MB15936A0B092F7467CC18B3C1D7419@MWHPR21MB1593.namprd21.prod.outlook.com>
Date:   Sun, 26 Dec 2021 19:49:41 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     YueHaibing <yuehaibing@...wei.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Long Li <longli@...rosoft.com>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH -next] scsi: storvsc: Fix unsigned comparison to zero

From: YueHaibing <yuehaibing@...wei.com> Sent: Friday, December 24, 2021 4:02 AM
> 
> The unsigned variable sg_count is being assigned a return value
> from the call to scsi_dma_map() that can return -ENOMEM.
> 
> Fixes: 743b237c3a7b ("scsi: storvsc: Add Isolation VM support for storvsc driver")
> Signed-off-by: YueHaibing <yuehaibing@...wei.com>

Good catch!  But I wonder if a simpler fix is to just remove the "unsigned"
from the declaration of sg_count.  Then we don't need to add the
sg_cnt local variable.  A little less complexity is almost always better. :-)

Michael

> ---
>  drivers/scsi/storvsc_drv.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index ae293600d799..072c752a8c36 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -1837,7 +1837,7 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
>  		unsigned int hvpg_count = HVPFN_UP(offset_in_hvpg + length);
>  		struct scatterlist *sg;
>  		unsigned long hvpfn, hvpfns_to_add;
> -		int j, i = 0;
> +		int sg_cnt, j, i = 0;
> 
>  		if (hvpg_count > MAX_PAGE_BUFFER_COUNT) {
> 
> @@ -1851,11 +1851,11 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
>  		payload->range.len = length;
>  		payload->range.offset = offset_in_hvpg;
> 
> -		sg_count = scsi_dma_map(scmnd);
> -		if (sg_count < 0)
> +		sg_cnt = scsi_dma_map(scmnd);
> +		if (sg_cnt < 0)
>  			return SCSI_MLQUEUE_DEVICE_BUSY;
> 
> -		for_each_sg(sgl, sg, sg_count, j) {
> +		for_each_sg(sgl, sg, sg_cnt, j) {
>  			/*
>  			 * Init values for the current sgl entry. hvpfns_to_add
>  			 * is in units of Hyper-V size pages. Handling the
> --
> 2.17.1