linux-kernel - Re: [PATCH v2] [SCSI] scsi

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Date:	Wed, 17 Jul 2013 00:21:38 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Paul Bolle <pebolle@...cali.nl>
Cc:	"James E.J. Bottomley" <JBottomley@...allels.com>,
	linux-scsi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Douglas Gilbert <dgilbert@...erlog.com>
Subject: Re: [PATCH v2] [SCSI] scsi_debug: silence GCC warning

2013/7/16 Paul Bolle <pebolle@...cali.nl>:
> Building scsi_debug.o triggers a GCC warning:
>     drivers/scsi/scsi_debug.c: In function ‘dif_verify’:
>     drivers/scsi/scsi_debug.c:1755:3: warning: ‘csum’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>
> This is a false positive. But if we transform the switch statement in
> dif_compute_csum() to a straightforward if/else statement we supply GCC
> with enough information to determine that csum will not be used
> uninitialized.
>
> Signed-off-by: Paul Bolle <pebolle@...cali.nl>
> ---
> 0) v2 because I started to worry whether v1 would change an interface
> (ie, the way the "guard" module parameter behaves). This patch is much
> simpler, and doesn't change any behavior.
>
> 1) Still only compile tested.

This one looks good to me.  It would be much better if this commit
log had a reference to the commit that introduced this warning as
you described after '---' in v1 patch.

>  drivers/scsi/scsi_debug.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index cb4fefa..7565ec5 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -1735,14 +1735,11 @@ static u16 dif_compute_csum(const void *buf, int len)
>  {
>         u16 csum;
>
> -       switch (scsi_debug_guard) {
> -       case 1:
> +       if (scsi_debug_guard == 1)
>                 csum = ip_compute_csum(buf, len);
> -               break;
> -       case 0:
> +       else
>                 csum = cpu_to_be16(crc_t10dif(buf, len));
> -               break;
> -       }
> +
>         return csum;
>  }
>
> --
> 1.8.1.4
>
> --
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