[FFmpeg-cvslog] avcodec: Fix invalid uses of ff_codec_open2_recursive()

Andreas Rheinhardt git at videolan.org
Fri Dec 4 17:40:54 EET 2020

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at gmail.com> | Thu Nov 26 23:16:04 2020 +0100| [4e1fee405f0cbe09747f548943c083f1dc91a19e] | committer: Andreas Rheinhardt

avcodec: Fix invalid uses of ff_codec_open2_recursive()

Normally no two codecs with FF_CODEC_CAP_INIT_THREADSAFE unset
can be initialized at the same time: a mutex in avcodec_open2()
ensures this. This implies that one cannot simply open a codec
with a non-threadsafe init-function from the init function of
a codec whose own init function is not threadsafe either as the child
codec couldn't acquire the lock.

ff_codec_open2_recursive() exists to get around this limitation:
If the init function of the child codec to be initialized is not
thread-safe, the mutex is unlocked, the child is initialized and
the mutex is locked again. This of course has as a prerequisite that
the parent AVCodecContext actually holds the lock, i.e. that the
parent codec's init function is not thread-safe. If it is, then one
can (and has to) just use avcodec_open2() directly (if the child's
init function is not thread-safe, then avcodec_open2() will have to
acquire the mutex itself (and potentially wait for it), so that it is
perfectly fine for an otherwise thread-safe init function to open
a codec with a potentially non-thread-safe init function via

Yet several of the users of ff_codec_open2_recursive() have the
FF_CODEC_CAP_INIT_THREADSAFE flag set; this only worked because
all the child codecs' init functions were thread-safe themselves
so that ff_codec_open2_recursive() didn't touch the mutex at all.
But of course the real solution to this is to directly use

Reviewed-by: Anton Khirnov <anton at khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=4e1fee405f0cbe09747f548943c083f1dc91a19e

 libavcodec/avrndec.c | 2 +-
 libavcodec/imm5.c    | 4 ++--
 libavcodec/tdsc.c    | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/libavcodec/avrndec.c b/libavcodec/avrndec.c
index c5a60acd4f..d85e3c2000 100644
--- a/libavcodec/avrndec.c
+++ b/libavcodec/avrndec.c
@@ -65,7 +65,7 @@ static av_cold int init(AVCodecContext *avctx)
         a->mjpeg_avctx->width = avctx->width;
         a->mjpeg_avctx->height = avctx->height;
-        if ((ret = ff_codec_open2_recursive(a->mjpeg_avctx, codec, &thread_opt)) < 0) {
+        if ((ret = avcodec_open2(a->mjpeg_avctx, codec, &thread_opt)) < 0) {
             av_log(avctx, AV_LOG_ERROR, "MJPEG codec failed to open\n");
diff --git a/libavcodec/imm5.c b/libavcodec/imm5.c
index 917b414e66..5f8faa4dd0 100644
--- a/libavcodec/imm5.c
+++ b/libavcodec/imm5.c
@@ -63,7 +63,7 @@ static av_cold int imm5_init(AVCodecContext *avctx)
     ctx->h264_avctx->thread_count = 1;
     ctx->h264_avctx->flags        = avctx->flags;
     ctx->h264_avctx->flags2       = avctx->flags2;
-    ret = ff_codec_open2_recursive(ctx->h264_avctx, codec, NULL);
+    ret = avcodec_open2(ctx->h264_avctx, codec, NULL);
     if (ret < 0)
         return ret;
@@ -76,7 +76,7 @@ static av_cold int imm5_init(AVCodecContext *avctx)
     ctx->hevc_avctx->thread_count = 1;
     ctx->hevc_avctx->flags        = avctx->flags;
     ctx->hevc_avctx->flags2       = avctx->flags2;
-    ret = ff_codec_open2_recursive(ctx->hevc_avctx, codec, NULL);
+    ret = avcodec_open2(ctx->hevc_avctx, codec, NULL);
     if (ret < 0)
         return ret;
diff --git a/libavcodec/tdsc.c b/libavcodec/tdsc.c
index dfd80f6dbc..7c888b6ec8 100644
--- a/libavcodec/tdsc.c
+++ b/libavcodec/tdsc.c
@@ -125,7 +125,7 @@ static av_cold int tdsc_init(AVCodecContext *avctx)
     ctx->jpeg_avctx->flags2 = avctx->flags2;
     ctx->jpeg_avctx->dct_algo = avctx->dct_algo;
     ctx->jpeg_avctx->idct_algo = avctx->idct_algo;
-    ret = ff_codec_open2_recursive(ctx->jpeg_avctx, codec, NULL);
+    ret = avcodec_open2(ctx->jpeg_avctx, codec, NULL);
     if (ret < 0)
         return ret;

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