linux-kernel - Re: [PATCH v2 1/2] mtd: nand: Error out if cmd

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Date:	Wed, 20 Jul 2016 10:10:29 -0700
From:	Andrey Smirnov <andrew.smirnov@...il.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	linux-mtd@...ts.infradead.org, Richard Weinberger <richard@....at>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mtd: nand: Error out if cmd_ctrl() is missing

On Tue, Jul 19, 2016 at 11:44 PM, Boris Brezillon
<boris.brezillon@...e-electrons.com> wrote:
> On Tue, 19 Jul 2016 22:33:57 -0700
> Andrey Smirnov <andrew.smirnov@...il.com> wrote:
>
>> 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. Same is true for
>> chip->cmdfunc().
>>
>> To avoid the above scenario change the prototype of nand_set_defaults()
>> to return error code, all the callers to check for it and error out if
>> cmd_ctrl() is not provided.
>>
>> Suggested-by: Brian Norris <computersforpeace@...il.com>
>> Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
>> ---
>>  drivers/mtd/nand/nand_base.c | 29 ++++++++++++++++++++++++-----
>>  1 file changed, 24 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
>> index ce7b2ca..bee480f 100644
>> --- a/drivers/mtd/nand/nand_base.c
>> +++ b/drivers/mtd/nand/nand_base.c
>> @@ -3114,22 +3114,30 @@ static void nand_shutdown(struct mtd_info *mtd)
>>  }
>>
>>  /* Set default functions */
>> -static void nand_set_defaults(struct nand_chip *chip, int busw)
>> +static int nand_set_defaults(struct nand_chip *chip, int busw)
>>  {
>>       /* check for proper chip_delay setup, set 20us if not */
>>       if (!chip->chip_delay)
>>               chip->chip_delay = 20;
>>
>>       /* check, if a user supplied command function given */
>> -     if (chip->cmdfunc == NULL)
>> +     if (chip->cmdfunc == NULL) {
>> +             if (!chip->cmd_ctrl)
>> +                     goto no_cmd_ctrl;
>> +
>>               chip->cmdfunc = nand_command;
>> +     }
>>
>>       /* check, if a user supplied wait function given */
>>       if (chip->waitfunc == NULL)
>>               chip->waitfunc = nand_wait;
>>
>> -     if (!chip->select_chip)
>> +     if (!chip->select_chip) {
>> +             if (!chip->cmd_ctrl)
>> +                     goto no_cmd_ctrl;
>> +
>>               chip->select_chip = nand_select_chip;
>> +     }
>>
>>       /* set for ONFI nand */
>>       if (!chip->onfi_set_features)
>> @@ -3161,6 +3169,11 @@ static void nand_set_defaults(struct nand_chip *chip, int busw)
>>               init_waitqueue_head(&chip->controller->wq);
>>       }
>>
>> +     return 0;
>> +
>> +no_cmd_ctrl:
>> +     pr_err("chip.cmd_ctrl() callback is not provided\n");
>> +     return -EINVAL;
>>  }
>>
>>  /* Sanitize ONFI strings so we can safely print them */
>> @@ -3878,9 +3891,13 @@ ident_done:
>>       }
>>
>>       if (chip->options & NAND_BUSWIDTH_AUTO) {
>> +             int ret;
>> +
>>               WARN_ON(chip->options & NAND_BUSWIDTH_16);
>>               chip->options |= busw;
>> -             nand_set_defaults(chip, busw);
>> +             ret = nand_set_defaults(chip, busw);
>
> I realize this one will actually never fail because it has already been
> checked in nand_scan_ident(). Maybe we should leave the
> nand_set_defaults() as a void function and check for missing
> ->cmd_ctrl() directly in nand_scan_ident().

Sure, will change in v3, this would also allow me to have only a
single check instead of two and those ugly gotos.

Andrey