linux-kernel - Re: [PATCH 6/8] spi: spi-s3c64xx: Check return values

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Date:   Wed, 19 Aug 2020 17:41:43 +0200
From:   Lukasz Stelmach <l.stelmach@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Kukjin Kim <kgene@...nel.org>, Andi Shyti <andi@...zian.org>,
        Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        m.szyprowski@...sung.com, b.zolnierkie@...sung.com
Subject: Re: [PATCH 6/8] spi: spi-s3c64xx: Check return values

It was <2020-08-19 śro 14:48>, when Krzysztof Kozlowski wrote:
> On Wed, Aug 19, 2020 at 02:32:06PM +0200, Łukasz Stelmach wrote:
>> Signed-off-by: Łukasz Stelmach <l.stelmach@...sung.com>
>> ---
>>  drivers/spi/spi-s3c64xx.c | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>
> Oh, come on, stop fixing the same local issue without fixing bigger
> picture... or at least documenting why bigger picture does not have to be
> fixed and simple 'return' is enough.
>
> That's the third, same fix for the same problem.
>
> https://lore.kernel.org/lkml/20190314064202.14864-1-kjlu@umn.edu/
> https://lore.kernel.org/lkml/20170207204520.h2eo3yn5kge56lk7@kozik-lap/

No wonder. There is a possible NULL dereference below. Now at least we
know something about conditions that led to this.

Should I drop the entire patch, or just the dmaengine_prep_slave_sg() part?


>> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
>> index 505789f91fdf..27d77600a820 100644
>> --- a/drivers/spi/spi-s3c64xx.c
>> +++ b/drivers/spi/spi-s3c64xx.c
>> @@ -273,6 +273,7 @@ static void prepare_dma(struct s3c64xx_spi_dma_data *dma,
>>  	struct s3c64xx_spi_driver_data *sdd;
>>  	struct dma_slave_config config;
>>  	struct dma_async_tx_descriptor *desc;
>> +	int ret;
>>  
>>  	memset(&config, 0, sizeof(config));
>>  
>> @@ -296,11 +297,22 @@ static void prepare_dma(struct s3c64xx_spi_dma_data *dma,
>>  
>>  	desc = dmaengine_prep_slave_sg(dma->ch, sgt->sgl, sgt->nents,
>>  				       dma->direction, DMA_PREP_INTERRUPT);
>> +	if (!desc) {
>> +		dev_err(&sdd->pdev->dev, "unable to prepare %s scatterlist",
>> +			dma->direction == DMA_DEV_TO_MEM ? "rx" : "tx");
>> +		return;
>> +	}
>>  
>>  	desc->callback = s3c64xx_spi_dmacb;
>>  	desc->callback_param = dma;
>>  
>>  	dma->cookie = dmaengine_submit(desc);
>> +	ret = dma_submit_error(dma->cookie);
>> +	if (ret) {
>> +		dev_err(&sdd->pdev->dev, "dmaengine_submit() failed %d", ret);
>> +		return;
>> +	}
>> +
>>  	dma_async_issue_pending(dma->ch);
>>  }
>>  
>> -- 
>> 2.26.2
>> 
>
>

-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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