linux-kernel - Re: [PATCH][next] scsi: lpfc: fix less than zero comparison on unsigned int computation

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Date:   Mon, 6 Jul 2020 07:48:16 -0700
From:   James Smart <james.smart@...adcom.com>
To:     Colin King <colin.king@...onical.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] scsi: lpfc: fix less than zero comparison on
 unsigned int computation


On 7/6/2020 6:08 AM, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
>
> The expressions start_idx - dbg_cnt is evaluated using unsigned int
> arthithmetic (since these variables are unsigned ints) and hence can
> never be less than zero, so the less than comparison is never true.
> Re-write the expression to check for start_idx being less than dbg_cnt.
>
> Addresses-Coverity: ("Unsigned compared against 0")
> Fixes: 372c187b8a70 ("scsi: lpfc: Add an internal trace log buffer")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>   drivers/scsi/lpfc/lpfc_init.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/lpfc/lpfc_init.c b/drivers/scsi/lpfc/lpfc_init.c
> index 7285b0114837..ce5afe7b11d0 100644
> --- a/drivers/scsi/lpfc/lpfc_init.c
> +++ b/drivers/scsi/lpfc/lpfc_init.c
> @@ -14152,7 +14152,7 @@ void lpfc_dmp_dbg(struct lpfc_hba *phba)
>   		if ((start_idx + dbg_cnt) > (DBG_LOG_SZ - 1)) {
>   			temp_idx = (start_idx + dbg_cnt) % DBG_LOG_SZ;
>   		} else {
> -			if ((start_idx - dbg_cnt) < 0) {
> +			if (start_idx < dbg_cnt) {
>   				start_idx = DBG_LOG_SZ - (dbg_cnt - start_idx);
>   				temp_idx = 0;
>   			} else {

Thanks Colin - I was about to send a patch for this. Has this fix and 
one a couple of lines further down. I will post it shortly.

-- james