linux-kernel - Re: [PATCH 2/6] amd/amdkfd: Ignore return code of dma_fence

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Message-ID: <5c69f4849cb3d9dc087c303a33ba385925e126eb.camel@mailbox.org>
Date: Thu, 27 Nov 2025 16:43:28 +0100
From: Philipp Stanner <phasta@...lbox.org>
To: "Kuehling, Felix" <felix.kuehling@....com>, Christian
 König <christian.koenig@....com>, phasta@...nel.org,
 Sumit Semwal <sumit.semwal@...aro.org>, Gustavo Padovan
 <gustavo@...ovan.org>, Alex Deucher <alexander.deucher@....com>, David
 Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Jani Nikula
 <jani.nikula@...ux.intel.com>, Joonas Lahtinen
 <joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
 Tvrtko Ursulin <tursulin@...ulin.net>, Huang Rui <ray.huang@....com>,
 Matthew Auld <matthew.auld@...el.com>,  Matthew Brost
 <matthew.brost@...el.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, Lucas De Marchi
 <lucas.demarchi@...el.com>, Thomas Hellström
 <thomas.hellstrom@...ux.intel.com>
Cc: linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org, 
	amd-gfx@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org, 
	intel-xe@...ts.freedesktop.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 2/6] amd/amdkfd: Ignore return code of dma_fence_signal()

On Thu, 2025-11-27 at 10:08 -0500, Kuehling, Felix wrote:
> On 2025-11-27 04:55, Christian König wrote:
> > On 11/27/25 10:48, Philipp Stanner wrote:
> > > 

[…]

> > > The issue now is that dma_fence_signal()'s return code is actually non-
> > > racy, because check + bit-set are protected by lock.
> > > 
> > > Christian's new spinlock series would add a lock function for fences:
> > > https://lore.kernel.org/dri-devel/20251113145332.16805-5-christian.koenig@amd.com/
> > > 
> > > 
> > > So I suppose this should work:
> > > 
> > > dma_fence_lock_irqsave(ef, flags);
> > > if (dma_fence_test_signaled_flag(ef)) {
> > > 	dma_fence_unlock_irqrestore(ef, flags);
> > > 	return true;
> > > }
> > > dma_fence_signal_locked(ef);
> > > dma_fence_unlock_irqrestore(ef, flags);
> > > 
> > > return false;
> > > 
> > > 
> > > + some cosmetic adjustments for the boolean of course.
> > > 
> > > 
> > > Would that fly and be reasonable? @Felix, Christian.
> > I was just about to reply with the same idea when your mail arrived.
> 
> I agree as well. The important feature is that we need to test and 
> signal the fence atomically. It may even make sense to add a function
> for that "dma_fence_test_and_signal" that preserves the original 
> behaviour of dma_fence_signal. ;)

Fine by me if the maintainer agrees

P.