linux-kernel - Re: [PATCH v2] drm/sched: Fix dynamic job-flow control race

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Message-ID: <Zu7Vnr7y4fS6KZaY@robin>
Date: Sat, 21 Sep 2024 16:18:06 +0200
From: Janne Grunau <janne@...nau.net>
To: Rob Clark <robdclark@...il.com>
Cc: dri-devel@...ts.freedesktop.org, Rob Clark <robdclark@...omium.org>,
	Asahi Lina <lina@...hilina.net>, stable@...r.kernel.org,
	Luben Tuikov <ltuikov89@...il.com>,
	Matthew Brost <matthew.brost@...el.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Danilo Krummrich <dakr@...hat.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/sched: Fix dynamic job-flow control race

On Fri, Sep 13, 2024 at 01:23:01PM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> Fixes a race condition reported here: https://github.com/AsahiLinux/linux/issues/309#issuecomment-2238968609
> 
> The whole premise of lockless access to a single-producer-single-
> consumer queue is that there is just a single producer and single
> consumer.  That means we can't call drm_sched_can_queue() (which is
> about queueing more work to the hw, not to the spsc queue) from
> anywhere other than the consumer (wq).
> 
> This call in the producer is just an optimization to avoid scheduling
> the consuming worker if it cannot yet queue more work to the hw.  It
> is safe to drop this optimization to avoid the race condition.
> 
> Suggested-by: Asahi Lina <lina@...hilina.net>
> Fixes: a78422e9dff3 ("drm/sched: implement dynamic job-flow control")
> Closes: https://github.com/AsahiLinux/linux/issues/309
> Cc: stable@...r.kernel.org
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/scheduler/sched_entity.c | 4 ++--
>  drivers/gpu/drm/scheduler/sched_main.c   | 7 ++-----
>  include/drm/gpu_scheduler.h              | 2 +-
>  3 files changed, 5 insertions(+), 8 deletions(-)

Tested for several hours with CONFIG_PREMPT=y and kasan with a similar
workload as in the github issue without reports or oopses.

Feel free to add
Tested-by: Janne Grunau <j@...nau.net>

thanks,
Janne