Quoting Lynne (2023-04-19 16:39:28) > Apr 17, 2023, 11:25 by an...@khirnov.net: > > > Quoting Lynne (2023-03-14 07:33:43) > > > >> From 6e2dfc44e50798264eb16bc2dcabfdbf2fbac2d7 Mon Sep 17 00:00:00 2001 > >> From: Lynne <d...@lynne.ee> > >> Date: Thu, 15 Dec 2022 01:06:52 +0100 > >> Subject: [PATCH 24/92] hwconfig: add a new HWACCEL_CAP_THREAD_SAFE for > >> threadsafe hwaccels > >> > >> Vulkan is fully threadsafe and stateless, so we can benefit from this. > >> --- > >> libavcodec/hwconfig.h | 1 + > >> libavcodec/pthread_frame.c | 2 +- > >> 2 files changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/libavcodec/hwconfig.h b/libavcodec/hwconfig.h > >> index 721424912c..e6b78f0160 100644 > >> --- a/libavcodec/hwconfig.h > >> +++ b/libavcodec/hwconfig.h > >> @@ -24,6 +24,7 @@ > >> > >> > >> #define HWACCEL_CAP_ASYNC_SAFE (1 << 0) > >> +#define HWACCEL_CAP_THREAD_SAFE (1 << 1) > >> > >> > >> typedef struct AVCodecHWConfigInternal { > >> diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c > >> index 74864e19c5..c096287233 100644 > >> --- a/libavcodec/pthread_frame.c > >> +++ b/libavcodec/pthread_frame.c > >> @@ -204,7 +204,7 @@ static attribute_align_arg void > >> *frame_worker_thread(void *arg) > >> > >> /* if the previous thread uses hwaccel then we take the lock to ensure > >> * the threads don't run concurrently */ > >> - if (avctx->hwaccel) { > >> + if (avctx->hwaccel && !(avctx->hwaccel->caps_internal & > >> HWACCEL_CAP_THREAD_SAFE)) { > >> > > > > A major problem here is that hwaccel_priv_data exists in only a single > > instance shared across all the worker threads. If you want frame-threaded > > hwaccels, you'll need to add some mechanism for synchronizing it between > > threads. > > > > I really wonder how does your code survive all the races involved. > > > > It works because hwaccel_priv_data is read-only. No need to synchronize > anything, the contexts Vulkan creates are defined as driver-synchronized, > and all the info a frame needs is provided when decoding it, rather than > kept as a state. > So I don't see a problem here.
>From a quick glance, at least vk_av1_free_frame_priv() modifies this context, which seems highly unsafe. This really seems like a disaster waiting to happen, there should be some stronger guarantees that nobody will modify this context when they shouldn't. -- Anton Khirnov _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".