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Thu, 13 Aug 2026 03:37:21 -0700 (PDT) Message-ID: <2dd34398-3ef2-4573-8311-60e5f6b346aa@ursulin.net> Date: Thu, 13 Aug 2026 11:37:20 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/sched: Lock drm_sched_entity_is_idle() To: Philipp Stanner , Matthew Brost , Danilo Krummrich , =?UTF-8?Q?Christian_K=C3=B6nig?= , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20260813094539.2407911-2-phasta@kernel.org> Content-Language: en-GB From: Tvrtko Ursulin In-Reply-To: <20260813094539.2407911-2-phasta@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 13/08/2026 10:45, Philipp Stanner wrote: > drm_sched_entity_is_idle() contains a badly documented memory barrier > and an invalid lockless access to entity->stopped. Moreover, it also > accesses entity->list which is at all other places protected by > entity->lock. > > This function is in no way performance critical, so it is safer, more > readable and more maintainable to take the spinlock. > > Add locking to drm_sched_entity_is_idle(). > > Signed-off-by: Philipp Stanner > --- > drivers/gpu/drm/scheduler/sched_entity.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c > index c51101ec70c1..2d941b2b2861 100644 > --- a/drivers/gpu/drm/scheduler/sched_entity.c > +++ b/drivers/gpu/drm/scheduler/sched_entity.c > @@ -179,14 +179,18 @@ EXPORT_SYMBOL(drm_sched_entity_modify_sched); > > static bool drm_sched_entity_is_idle(struct drm_sched_entity *entity) > { > - rmb(); /* for list_empty to work without lock */ > + bool idle = false; > + > + spin_lock(&entity->lock); > > if (list_empty(&entity->list) || > spsc_queue_count(&entity->job_queue) == 0 || > entity->stopped) > - return true; > + idle = true; > > - return false; > + spin_unlock(&entity->lock); > + > + return idle; > } > > /** > > base-commit: c9a2c8ddcd65e96e7f095a87c0cc0b3211f740ea Spotted by chance on the mailing list but I believe I gave you r-b for this one already. Regards, Tvrtko