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

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Date:   Wed, 13 Dec 2017 20:44:45 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.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 13/12/17 20:38, Boris Brezillon wrote:
> 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.

I see my mistake, I fixed the *wrong* function, I'll send a v2. Doh.
> 
> [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);
>>>>  	}
>>>>    
>>>   
>>
> 
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