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authorAndreas Rheinhardt <andreas.rheinhardt@outlook.com>2021-09-18 05:11:57 +0200
committerAndreas Rheinhardt <andreas.rheinhardt@outlook.com>2021-09-19 23:52:37 +0200
commitf440c422b70ce76f225a34ebf168215a432e8d88 (patch)
tree62b8c418d5724ca8697f23871931a9053f4b8b09 /libswscale/swscale.c
parenta1255a350d4629ca9f0073289ae8e2862aa0d9e1 (diff)
downloadffmpeg-f440c422b70ce76f225a34ebf168215a432e8d88.tar.gz
swscale/swscale: Fix races when using unaligned strides/data
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 the nv12, nv21, yuv420, yuv420p10, yuv422, yuv422p10 and yuv444 filter-overlay FATE-tests. Reviewed-by: Michael Niedermayer <michael@niedermayer.cc> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Diffstat (limited to 'libswscale/swscale.c')
-rw-r--r--libswscale/swscale.c12
1 files changed, 6 insertions, 6 deletions
diff --git a/libswscale/swscale.c b/libswscale/swscale.c
index b9c9647fcb..040172752f 100644
--- a/libswscale/swscale.c
+++ b/libswscale/swscale.c
@@ -312,12 +312,12 @@ static int swscale(SwsContext *c, const uint8_t *src[],
if (dstStride[0]&15 || dstStride[1]&15 ||
dstStride[2]&15 || dstStride[3]&15) {
- static int warnedAlready = 0; // FIXME maybe move this into the context
- if (flags & SWS_PRINT_INFO && !warnedAlready) {
+ SwsContext *const ctx = c->parent ? c->parent : c;
+ if (flags & SWS_PRINT_INFO &&
+ !atomic_exchange_explicit(&ctx->stride_unaligned_warned, 1, memory_order_relaxed)) {
av_log(c, AV_LOG_WARNING,
"Warning: dstStride is not aligned!\n"
" ->cannot do aligned memory accesses anymore\n");
- warnedAlready = 1;
}
}
@@ -326,11 +326,11 @@ static int swscale(SwsContext *c, const uint8_t *src[],
|| dstStride[0]&15 || dstStride[1]&15 || dstStride[2]&15 || dstStride[3]&15
|| srcStride[0]&15 || srcStride[1]&15 || srcStride[2]&15 || srcStride[3]&15
) {
- static int warnedAlready=0;
+ SwsContext *const ctx = c->parent ? c->parent : c;
int cpu_flags = av_get_cpu_flags();
- if (HAVE_MMXEXT && (cpu_flags & AV_CPU_FLAG_SSE2) && !warnedAlready){
+ if (HAVE_MMXEXT && (cpu_flags & AV_CPU_FLAG_SSE2) &&
+ !atomic_exchange_explicit(&ctx->stride_unaligned_warned,1, memory_order_relaxed)) {
av_log(c, AV_LOG_WARNING, "Warning: data is not aligned! This can lead to a speed loss\n");
- warnedAlready=1;
}
}