From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id B212543AED for ; Sat, 22 Apr 2023 12:42:02 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id A6CE068BF45; Sat, 22 Apr 2023 15:41:59 +0300 (EEST) Received: from mail0.khirnov.net (red.khirnov.net [176.97.15.12]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id D7A5468B2BC for ; Sat, 22 Apr 2023 15:41:53 +0300 (EEST) Received: from localhost (localhost [IPv6:::1]) by mail0.khirnov.net (Postfix) with ESMTP id 95CE52404EE for ; Sat, 22 Apr 2023 14:41:53 +0200 (CEST) Received: from mail0.khirnov.net ([IPv6:::1]) by localhost (mail0.khirnov.net [IPv6:::1]) (amavisd-new, port 10024) with ESMTP id t7_jTYP99I9d for ; Sat, 22 Apr 2023 14:41:52 +0200 (CEST) Received: from lain.khirnov.net (lain.khirnov.net [IPv6:2001:67c:1138:4306::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "lain.khirnov.net", Issuer "smtp.khirnov.net SMTP CA" (verified OK)) by mail0.khirnov.net (Postfix) with ESMTPS id 5CA352404EC for ; Sat, 22 Apr 2023 14:41:52 +0200 (CEST) Received: by lain.khirnov.net (Postfix, from userid 1000) id 3F6831601B2; Sat, 22 Apr 2023 14:41:52 +0200 (CEST) From: Anton Khirnov To: FFmpeg development discussions and patches In-Reply-To: References: <168172351803.3843.891431528072089458@lain.khirnov.net> Mail-Followup-To: FFmpeg development discussions and patches Date: Sat, 22 Apr 2023 14:41:52 +0200 Message-ID: <168216731222.3843.7711457127740646229@lain.khirnov.net> User-Agent: alot/0.8.1 MIME-Version: 1.0 Subject: Re: [FFmpeg-devel] [PATCH 31/92] Vulkan patchset part 1 - common code changes X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: Quoting Lynne (2023-04-19 16:39:28) > Apr 17, 2023, 11:25 by anton@khirnov.net: > > > Quoting Lynne (2023-03-14 07:33:43) > > > >> From 6e2dfc44e50798264eb16bc2dcabfdbf2fbac2d7 Mon Sep 17 00:00:00 2001 > >> From: Lynne > >> 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-request@ffmpeg.org with subject "unsubscribe".