linux-kernel - Re: [PATCH] mtd: spi-nor: stm32-quadspi: Fix uninitialized error return code

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Message-ID: <ca80511a-794f-eb74-38a9-be15d48f9e20@st.com>
Date:   Fri, 15 Sep 2017 12:06:39 +0200
From:   Ludovic BARRE <ludovic.barre@...com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Marek Vasut <marek.vasut@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Arnd Bergmann <arnd@...db.de>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mtd: spi-nor: stm32-quadspi: Fix uninitialized error
 return code



On 07/17/2017 12:22 PM, Geert Uytterhoeven wrote:
> Hi Ludovic,
> 
> On Mon, Jul 17, 2017 at 11:56 AM, Ludovic BARRE <ludovic.barre@...com> wrote:
>> Today only write_reg could be call with len=0 (spi-nor.c:
>> write_enable/disable, set_4byte, erase_chip)
>>
>> But your remark make sense to prevent: gcc warning and framework evolution
>> ...
>>
>>
>> -In stm32-quadspi.c transfer data is enabled if tx_data is true (some
>> actions under this bool)
>>
>> stm32_qspi_write_reg has already this protection with "!!(buf && len > 0);"
>>
>> but we could extend this protection
>>
>> -    cmd.tx_data = true;
>> +    cmd.tx_data = !!(len > 0);
>>
>> In : stm32_qspi_read, stm32_qspi_write, stm32_qspi_read_reg
> 
> Ah, I missed the check for !cmd->tx_data at the top of stm32_qspi_tx()
> 
>> -And to avoid gcc warning: I prefer initialize "ret" in the beginning of
>> function
>>
>> -    int ret;
>> +    int ret = 0;
>>
>> I tested this changes, and it's ok for me.
>>
>> Geert could you resend a new version, or do you prefer that I take care of
>> it
> 
> If you initialized ret at the beginning, you lose the ability to catch newly
> introduced similar bugs in the future.
like discuss in thread https://patchwork.kernel.org/patch/9952849/ with 
Arnd and Geert

Cyrille, Marek: could you take geert patch and abandon
https://patchwork.kernel.org/patch/9952849/
thanks

Acked-by: Ludovic Barre <ludovic.barre@...com>

> 
>> On 07/15/2017 10:00 AM, Geert Uytterhoeven wrote:
>>>
>>> With gcc 4.1.2:
>>>
>>>       drivers/mtd/spi-nor/stm32-quadspi.c: In function
>>> ‘stm32_qspi_tx_poll’:
>>>       drivers/mtd/spi-nor/stm32-quadspi.c:230: warning: ‘ret’ may be used
>>> uninitialized in this function
>>>
>>> Indeed, if stm32_qspi_cmd.len is zero, ret will be uninitialized.
>>> This length is passed from outside the driver using the
>>> spi_nor.{read,write}{,_reg}() callbacks.
>>>
>>> Several functions in drivers/mtd/spi-nor/spi-nor.c (e.g. write_enable(),
>>> write_disable(), and erase_chip()) call spi_nor.write_reg() with a zero
>>> length.
>>>
>>> Fix this by returning an explicit zero on success.
>>>
>>> Fixes: 0d43d7ab277a048c ("mtd: spi-nor: add driver for STM32 quad spi
>>> flash controller")
>>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>>> ---
>>>    drivers/mtd/spi-nor/stm32-quadspi.c | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/mtd/spi-nor/stm32-quadspi.c
>>> b/drivers/mtd/spi-nor/stm32-quadspi.c
>>> index 86c0931543c538c3..ad6a3e1844cbe5ec 100644
>>> --- a/drivers/mtd/spi-nor/stm32-quadspi.c
>>> +++ b/drivers/mtd/spi-nor/stm32-quadspi.c
>>> @@ -240,12 +240,12 @@ static int stm32_qspi_tx_poll(struct stm32_qspi
>>> *qspi,
>>>
>>> STM32_QSPI_FIFO_TIMEOUT_US);
>>>                  if (ret) {
>>>                          dev_err(qspi->dev, "fifo timeout (stat:%#x)\n",
>>> sr);
>>> -                       break;
>>> +                       return ret;
>>>                  }
>>>                  tx_fifo(buf++, qspi->io_base + QUADSPI_DR);
>>>          }
>>>    -     return ret;
>>> +       return 0;
>>>    }
>>>      static int stm32_qspi_tx_mm(struct stm32_qspi *qspi,
> 
> Gr{oetje,eeting}s,
> 
>                          Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                  -- Linus Torvalds
>