linux-kernel - Re: [PATCH][mtd-next] mtd: nand: remove redundant check of len

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Date:   Wed, 13 Dec 2017 21:38:44 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-mtd@...ts.infradead.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][mtd-next] mtd: nand: remove redundant check of len

On Wed, 13 Dec 2017 20:30:04 +0000
Colin Ian King <colin.king@...onical.com> wrote:

> On 13/12/17 20:24, Boris Brezillon wrote:
> > On Wed, 13 Dec 2017 20:17:43 +0000
> > Colin King <colin.king@...onical.com> wrote:
> >   
> >> From: Colin Ian King <colin.king@...onical.com>
> >>
> >> The check of len being zero is redundant as it has already been
> >> sanity checked for this value at the start of the function. Hence
> >> it is impossible for this test to be true and so the redundant
> >> code can be removed.  
> > 
> > Nope, it's not the same test, the initial test is
> > 
> > 	if (len && !buf)  
> 
> Ah, the current tip from linux-next has:
> 
> 1912        if (!len || !buf)
> 1913                return -EINVAL;
> 
> ..so I guess that's why it got picked up by static analysis.

Hm, that's weird, that's not what I see [1] in linux-next.

[1]https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/mtd/nand/nand_base.c#n1488

> 
> > 
> > not
> > 
> > 	if (len)
> > 
> > So this test is not redundant.
> >   
> >>
> >> Detected by CoverityScan, CID#1462748 ("Logically dead code")
> >>
> >> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> >> ---
> >>  drivers/mtd/nand/nand_base.c | 4 ----
> >>  1 file changed, 4 deletions(-)
> >>
> >> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> >> index afd5e18db81c..9daaa23db943 100644
> >> --- a/drivers/mtd/nand/nand_base.c
> >> +++ b/drivers/mtd/nand/nand_base.c
> >> @@ -1507,10 +1507,6 @@ static int nand_read_param_page_op(struct nand_chip *chip, u8 page, void *buf,
> >>  		};
> >>  		struct nand_operation op = NAND_OPERATION(instrs);
> >>  
> >> -		/* Drop the DATA_IN instruction if len is set to 0. */
> >> -		if (!len)
> >> -			op.ninstrs--;
> >> -
> >>  		return nand_exec_op(chip, &op);
> >>  	}
> >>    
> >   
>