linux-kernel - Re: [PATCH] dma-buf: Don't use typeof in va

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Message-ID: <7a689b6c-31b7-61d2-7bf4-6fdf49bb4ae4@vivo.com>
Date:   Fri, 10 Jun 2022 15:52:39 +0800
From:   Jiabing Wan <wanjiabing@...o.com>
To:     Christian König <christian.koenig@....com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-buf: Don't use typeof in va_arg



On 2022/6/10 15:24, Christian König wrote:
> Am 10.06.22 um 09:20 schrieb Wan Jiabing:
>> Fix following coccicheck warning:
>> ./drivers/dma-buf/st-dma-fence-unwrap.c:75:39-45: ERROR: reference 
>> preceded by free on line 70
>>
>> Use 'struct dma_fence *' instead of 'typeof(*fences)' to avoid this
>> warning and also fix other 'typeof(*fences)' to make them consistent.
>
> Well that doesn't looks correct to me.
>
> *fence should be valid at this point, why does coccicheck things it is 
> freed?

*fence is valid. Coccicheck reports this because fence is freed.
But use 'struct dma_fence *' can avoid this wrong report.

I also grep all code and find it's unusual to use 'typeof' in va_arg, 
only two files.

grep -R "va_arg("  . | grep 'typeof'
./drivers/dma-buf/st-dma-fence-unwrap.c:                fences[i] = 
va_arg(valist, typeof(*fences));
./drivers/dma-buf/st-dma-fence-unwrap.c: dma_fence_put(va_arg(valist, 
typeof(*fences)));
./lib/test_scanf.c:             typeof(*expect) got = *va_arg(ap, 
typeof(expect));              \

And other files all use declaration name directly.
So I send this patch makes code clearer and fix the wrong warning by the 
way.

Thanks,
Wan Jiabing

>
> Regards,
> Christian.
>
>>
>> Fixes: 0c5064fa8d5a ("dma-buf: cleanup dma_fence_unwrap selftest v2")
>> Signed-off-by: Wan Jiabing <wanjiabing@...o.com>
>> ---
>>   drivers/dma-buf/st-dma-fence-unwrap.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c 
>> b/drivers/dma-buf/st-dma-fence-unwrap.c
>> index 4105d5ea8dde..1137a6d90b32 100644
>> --- a/drivers/dma-buf/st-dma-fence-unwrap.c
>> +++ b/drivers/dma-buf/st-dma-fence-unwrap.c
>> @@ -56,7 +56,7 @@ static struct dma_fence *mock_array(unsigned int 
>> num_fences, ...)
>>         va_start(valist, num_fences);
>>       for (i = 0; i < num_fences; ++i)
>> -        fences[i] = va_arg(valist, typeof(*fences));
>> +        fences[i] = va_arg(valist, struct dma_fence *);
>>       va_end(valist);
>>         array = dma_fence_array_create(num_fences, fences,
>> @@ -72,7 +72,7 @@ static struct dma_fence *mock_array(unsigned int 
>> num_fences, ...)
>>   error_put:
>>       va_start(valist, num_fences);
>>       for (i = 0; i < num_fences; ++i)
>> -        dma_fence_put(va_arg(valist, typeof(*fences)));
>> +        dma_fence_put(va_arg(valist, struct dma_fence *));
>>       va_end(valist);
>>       return NULL;
>>   }
>