[FFmpeg-devel] [PATCH] libavcodec/mpeg12dec: Use atomic addition for value updated in multiple threads.

[Nick Lewycky]

Sorry! Let's try an attachment then.

On 16 November 2017 at 14:36, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> On Thu, Nov 16, 2017 at 12:41:32PM -0800, Nick Lewycky wrote:
>> I initially discovered a signed integer overflow on this line. Since
>> this value is updated in multiple threads, I use an atomic update and
>> as it happens atomic addition is defined to wrap around. However,
>> there's still a potential bug in that the error_count may wrap around
>> and equal zero again causing problems down the line.
>>
>> ---
>>  libavcodec/mpeg12dec.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
>> index d5bc5f21b2..b7c3b5106e 100644
>> --- a/libavcodec/mpeg12dec.c
>> +++ b/libavcodec/mpeg12dec.c
>> @@ -28,6 +28,7 @@
>>  #define UNCHECKED_BITSTREAM_READER 1
>>  #include <inttypes.h>
>>
>> +#include "libavutil/atomic.h"
>>  #include "libavutil/attributes.h"
>>  #include "libavutil/imgutils.h"
>>  #include "libavutil/internal.h"
>> @@ -2476,7 +2477,7 @@ static int decode_chunks(AVCodecContext *avctx,
>> AVFrame *picture,
>>                                     &s2->thread_context[0], NULL,
>>                                     s->slice_count, sizeof(void *));
>>                      for (i = 0; i < s->slice_count; i++)
>> -                        s2->er.error_count +=
>> s2->thread_context[i]->er.error_count;
>> +
>> avpriv_atomic_int_add_and_fetch(&s2->er.error_count,
>> s2->thread_context[i]->er.error_count);
>>                  }
>
> This patch is corrupted by newlines
>
> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Dictatorship naturally arises out of democracy, and the most aggravated
> form of tyranny and slavery out of the most extreme liberty. -- Plato
>
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