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Tue, 1 Jul 2025 07:40:11 +0000 Message-ID: <8b288dcd-81ed-4047-89b4-4bc8a4062fb2@amd.com> Date: Tue, 1 Jul 2025 09:40:05 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/sched: Increment job count before swapping tail spsc queue To: Matthew Brost , intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org Cc: dakr@kernel.org, pstanner@redhat.com References: <20250613212013.719312-1-matthew.brost@intel.com> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20250613212013.719312-1-matthew.brost@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BL0PR02CA0073.namprd02.prod.outlook.com (2603:10b6:208:51::14) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|PH0PR12MB5607:EE_ X-MS-Office365-Filtering-Correlation-Id: 4215cbcd-45dd-4b53-17fa-08ddb8728299 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7053199007; 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If this race occurs, job > scheduling stops, leading to hangs while waiting on the job’s DMA > fences. > > Seal this race by incrementing the job count before appending to the > SPSC queue. > > This race was observed on a drm-tip 6.16-rc1 build with the Xe driver in > an SVM test case. > > Fixes: 1b1f42d8fde4 ("drm: move amd_gpu_scheduler into common location") > Fixes: 27105db6c63a ("drm/amdgpu: Add SPSC queue to scheduler.") > Cc: stable@vger.kernel.org > Signed-off-by: Matthew Brost Sorry for the late response, if it isn't already pushed to drm-misc-fixes then feel free to add Reviewed-by: Christian König > --- > include/drm/spsc_queue.h | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/include/drm/spsc_queue.h b/include/drm/spsc_queue.h > index 125f096c88cb..ee9df8cc67b7 100644 > --- a/include/drm/spsc_queue.h > +++ b/include/drm/spsc_queue.h > @@ -70,9 +70,11 @@ static inline bool spsc_queue_push(struct spsc_queue *queue, struct spsc_node *n > > preempt_disable(); > > + atomic_inc(&queue->job_count); > + smp_mb__after_atomic(); > + > tail = (struct spsc_node **)atomic_long_xchg(&queue->tail, (long)&node->next); > WRITE_ONCE(*tail, node); > - atomic_inc(&queue->job_count); > > /* > * In case of first element verify new node will be visible to the consumer