[FFmpeg-devel] [PATCH 2/3] swscale/swscale: Fix races when using unaligned strides/data

[Michael Niedermayer]

On Sat, Sep 18, 2021 at 05:43:25AM +0200, Andreas Rheinhardt wrote:
> In this case the current code tries to warn once; to do so, it uses
> ordinary static ints to store whether the warning has already been
> emitted. This is both a data race (and therefore undefined behaviour)
> as well as a race condition, because it is really possible for multiple
> threads to be the one thread to emit the warning. This is actually
> common since the introduction of the new multithreaded scaling API.
> 
> This commit fixes this by using atomic integers for the state;
> furthermore, these are not static anymore, but rather contained
> in the user-facing SwsContext (i.e. the parent SwsContext in case
> of slice-threading).
> 
> Given that these atomic variables are not intended for synchronization
> at all (but only for atomicity, i.e. only to output the warning once),
> the atomic operations use memory_order_relaxed.
> 
> This affected nv12, nv21, yuv420, yuv420p10, yuv422, yuv422p10 and
> yuv444 filter-overlay FATE-tests.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
> ---
> Of course, one could also use static atomic integers.

should be ok

thx

[...]
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