From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-101.mailbox.org (mout-p-101.mailbox.org [80.241.56.151]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D3F3225EF89; Wed, 9 Apr 2025 14:02:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.151 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744207341; cv=none; b=f1FjDT+n4GBY17Nt3PRQI4afh02zXoZ87kU7/w3O9fxUT1wJTVWXcQunB/Dk3iJQ3rf9nO8OAn1br5Ko1eGGiG1GR44xVxYeLT4IGpEcuw2ASq4l9D22XsQ0//+778AUz4U69WY/8wKzDWB4y5aiORr+1yg8dCgn+5OFrensTLw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744207341; c=relaxed/simple; bh=iqjOv8PC0paDWXrZO/qp2lqr+5gHSa2tmgVreDdK328=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=KujvkM61Vpzf5zVEdGPVJ8irXbaLZJsBKJASSpRDUngUqEhiz5jDugwK/FkGupmAw/FX0wT7el5JItR894rv2sjQezUjPFKG9aB+TSxv3COmR7OWAbzHY52W+nkcUho3YB+IKaQzCrp47tfFJNahumlOxMxJVBYIy8qy9gvh1Mo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org; spf=pass smtp.mailfrom=mailbox.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b=n/cAWajK; arc=none smtp.client-ip=80.241.56.151 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mailbox.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b="n/cAWajK" Received: from smtp102.mailbox.org (smtp102.mailbox.org [IPv6:2001:67c:2050:b231:465::102]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-101.mailbox.org (Postfix) with ESMTPS id 4ZXl4d5KM8z9t40; Wed, 9 Apr 2025 16:02:09 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1744207329; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iqjOv8PC0paDWXrZO/qp2lqr+5gHSa2tmgVreDdK328=; b=n/cAWajK7qyRBy39EjI+b038v5TLRQPnbsZsejuWIaDQc3yApnamzQUBNqrfVLqU+9ZQye 6YpZVyo+OPDJz8NnfwsjQkW1/y6T8ZXZ+VLyctnAx72cqilgUW+SYicNGsaZA5TL+OzNkv QVF2Uea5+pUcJ7Fh+KIO33qILuncMa8X7a+IkAFGK5lPYm43ATHvHa1QVFMEw5hX2abTeb Tjn7lStQsc8TA3pTDXqoh9lw6zAElg6K77S+v+XeIWrNUv24tD0L10jARdiINKJ+2S1/ec Ao1Sl7C7xYWCCuI7vapAaNwcVLexZ2Zq1R9aiaCivJq+ddQFc3xqeKqzfLnK9w== Message-ID: <9a90f7f14c22c01aa28d89aa91bf4dfa4049c062.camel@mailbox.org> Subject: Re: [PATCH 1/2] dma-fence: Rename dma_fence_is_signaled() From: Philipp Stanner Reply-To: phasta@kernel.org To: Christian =?ISO-8859-1?Q?K=F6nig?= , phasta@kernel.org, Boris Brezillon Cc: Sumit Semwal , Gustavo Padovan , Felix Kuehling , Alex Deucher , Xinhui Pan , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Lucas Stach , Russell King , Christian Gmeiner , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Frank Binns , Matt Coster , Qiang Yu , Rob Clark , Sean Paul , Konrad Dybcio , Abhinav Kumar , Dmitry Baryshkov , Marijn Suijten , Lyude Paul , Danilo Krummrich , Rob Herring , Steven Price , Dave Airlie , Gerd Hoffmann , Matthew Brost , Huang Rui , Matthew Auld , Melissa Wen , =?ISO-8859-1?Q?Ma=EDra?= Canal , Zack Rusin , Broadcom internal kernel review list , Lucas De Marchi , Thomas =?ISO-8859-1?Q?Hellstr=F6m?= , Bas Nieuwenhuizen , Yang Wang , Jesse Zhang , Tim Huang , Sathishkumar S , Saleemkhan Jamadar , Sunil Khatri , Lijo Lazar , Hawking Zhang , Ma Jun , Yunxiang Li , Eric Huang , Asad Kamal , Srinivasan Shanmugam , Jack Xiao , Friedrich Vock , Michel =?ISO-8859-1?Q?D=E4nzer?= , Geert Uytterhoeven , Anna-Maria Behnsen , Thomas Gleixner , Frederic Weisbecker , Dan Carpenter , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, etnaviv@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, lima@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org, nouveau@lists.freedesktop.org, virtualization@lists.linux.dev, spice-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org Date: Wed, 09 Apr 2025 16:01:53 +0200 In-Reply-To: References: <20250409120640.106408-2-phasta@kernel.org> <20250409120640.106408-3-phasta@kernel.org> <20250409143917.31303d22@collabora.com> <73d41cd84c73b296789b654e45125bfce88e0dbf.camel@mailbox.org> <72eb974dfea8fa1167cf97e29848672223f6fc5b.camel@mailbox.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MBO-RS-META: 46noetswqbs4h4jeiqeiz488uzz7697a X-MBO-RS-ID: 65a997a3aec7032e9b6 On Wed, 2025-04-09 at 15:14 +0200, Christian K=C3=B6nig wrote: > Am 09.04.25 um 14:56 schrieb Philipp Stanner: > > On Wed, 2025-04-09 at 14:51 +0200, Philipp Stanner wrote: > > > On Wed, 2025-04-09 at 14:39 +0200, Boris Brezillon wrote: > > > > Hi Philipp, > > > >=20 > > > > On Wed,=C2=A0 9 Apr 2025 14:06:37 +0200 > > > > Philipp Stanner wrote: > > > >=20 > > > > > dma_fence_is_signaled()'s name strongly reads as if this > > > > > function > > > > > were > > > > > intended for checking whether a fence is already signaled. > > > > > Also > > > > > the > > > > > boolean it returns hints at that. > > > > >=20 > > > > > The function's behavior, however, is more complex: it can > > > > > check > > > > > with a > > > > > driver callback whether the hardware's sequence number > > > > > indicates > > > > > that > > > > > the fence can already be treated as signaled, although the > > > > > hardware's / > > > > > driver's interrupt handler has not signaled it yet. If that's > > > > > the > > > > > case, > > > > > the function also signals the fence. > > > > >=20 > > > > > (Presumably) this has caused a bug in Nouveau (unknown > > > > > commit), > > > > > where > > > > > nouveau_fence_done() uses the function to check a fence, > > > > > which > > > > > causes a > > > > > race. > > > > >=20 > > > > > Give the function a more obvious name. > > > > This is just my personal view on this, but I find the new name > > > > just > > > > as > > > > confusing as the old one. It sounds like something is checked, > > > > but > > > > it's > > > > clear what, and then the fence is forcibly signaled like it > > > > would > > > > be > > > > if > > > > you call drm_fence_signal(). Of course, this clarified by the > > > > doc, > > > > but > > > > given the goal was to make the function name clearly reflect > > > > what > > > > it > > > > does, I'm not convinced it's significantly better. > > > >=20 > > > > Maybe dma_fence_check_hw_state_and_propagate(), though it might > > > > be > > > > too long of name. Oh well, feel free to ignore this comments if > > > > a > > > > majority is fine with the new name. > > > Yoa, the name isn't perfect (the perfect name describing the > > > whole > > > behavior would be > > > dma_fence_check_if_already_signaled_then_check_hardware_state_and > > > _pro > > > pa > > > gate() ^^' > > >=20 > > > My intention here is to have the reader realize "watch out, the > > > fence > > > might get signaled here!", which is probably the most important > > > event > > > regarding fences, which can race, invoke the callbacks and so on. > > >=20 > > > For details readers will then check the documentation. > > >=20 > > > But I'm of course open to see if there's a majority for this or > > > that > > > name. > > how about: > >=20 > > dma_fence_check_hw_and_signal() ? >=20 > I don't think that renaming the function is a good idea in the first > place. >=20 > What the function does internally is an implementation detail of the > framework. >=20 > For the code using this function it's completely irrelevant if the > function might also signal the fence, what matters for the caller is > the returned status of the fence. I think this also counts for the > dma_fence_is_signaled() documentation. It does obviously matter. As it's currently implemented, a lot of important things happen implicitly. I only see improvement by making things more obvious. In any case, how would you call a wrapper that just does test_bit(IS_SIGNALED, =E2=80=A6) ? P. >=20 > What we should improve is the documentation of the dma_fence_ops- > >enable_signaling and dma_fence_ops->signaled callbacks. >=20 > Especially see the comment about reference counts on enable_signaling > which is missing on the signaled callback. That is most likely the > root cause why nouveau implemented enable_signaling correctly but not > the other one. >=20 > But putting that aside I think we should make nails with heads and > let the framework guarantee that the fences stay alive until they are > signaled (one way or another). This completely removes the burden to > keep a reference on unsignaled fences from the drivers / > implementations and make things more over all more defensive. >=20 > Regards, > Christian. >=20 > >=20 > > P. > >=20 > > > P. > > >=20 > > >=20 > > > > Regards, > > > >=20 > > > > Boris >=20