linux-kernel - Re: [PATCH 1/2] mtd: nand: BUG_ON in case of no select_chip and cmd

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Date:	Tue, 19 Jul 2016 18:02:27 +0200
From:	Richard Weinberger <richard@....at>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	Andrey Smirnov <andrew.smirnov@...il.com>,
	linux-mtd@...ts.infradead.org,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mtd: nand: BUG_ON in case of no select_chip and
 cmd_ctrl

Am 19.07.2016 um 17:59 schrieb Boris Brezillon:
> On Tue, 19 Jul 2016 17:44:48 +0200
> Richard Weinberger <richard@....at> wrote:
> 
>> Am 19.07.2016 um 17:41 schrieb Andrey Smirnov:
>>> If no user specified chip->select_chip() function is provided, code in
>>> nand_base.c will automatically set this hook to nand_select_chip(),
>>> which in turn depends on chip->cmd_ctrl() hook being valid. Not
>>> providing both of those functions in NAND controller driver (for example
>>> by mistake) will result in a bit cryptic segfault. Replace it with
>>> explicit BUG_ON statement so it would be obvious what went wrong.
>>>
>>> Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
>>> ---
>>>  drivers/mtd/nand/nand_base.c | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
>>> index ce7b2ca..57043a6 100644
>>> --- a/drivers/mtd/nand/nand_base.c
>>> +++ b/drivers/mtd/nand/nand_base.c
>>> @@ -3128,8 +3128,10 @@ static void nand_set_defaults(struct nand_chip *chip, int busw)
>>>  	if (chip->waitfunc == NULL)
>>>  		chip->waitfunc = nand_wait;
>>>  
>>> -	if (!chip->select_chip)
>>> +	if (!chip->select_chip) {
>>> +		BUG_ON(!chip->cmd_ctrl);  
>>
>> Please don't add new BUG_ON() calls. WARN_ON() is good enough to raise the driver developer's
>> attention and won't kill the machine.
> 
> Not sure a BUG_ON() is worst than a NULL-pointer exception ;-).

When this really just triggers a NULL-pointer exception, we don't need a BUG_ON or WARN_ON at
all since the kernel can tell anyway what went wrong.

>From the patch description I thought it is a more cryptic problem...

Thanks,
//richard