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Fri, 07 Nov 2025 07:18:09 -0800 (PST) Message-ID: Date: Fri, 7 Nov 2025 15:18:08 +0000 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: Don't crash kernel on wrong params From: Tvrtko Ursulin 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: <20251107125508.235449-2-phasta@kernel.org> Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 07/11/2025 14:42, Tvrtko Ursulin wrote: > > On 07/11/2025 12:55, Philipp Stanner wrote: >> drm_sched_job_arm() just panics the kernel with BUG_ON() in case of an >> entity being NULL. While drm_sched_job_arm() crashing or not effectively >> arming jobs is certainly a huge issue that needs to be noticed, >> completely shooting down the kernel reduces the probability of reaching >> and debugging a system to 0. >> >> Moreover, the checkpatch script by now strongly discourages all new uses >> of BUG_ON() for this reason. >> >> Replace the BUG_ON() in drm_sched_job_arm() with a WARN_ON(). >> >> Signed-off-by: Philipp Stanner >> --- >>   drivers/gpu/drm/scheduler/sched_main.c | 2 +- >>   1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/ >> scheduler/sched_main.c >> index 1d4f1b822e7b..3bf4ae0ca4bc 100644 >> --- a/drivers/gpu/drm/scheduler/sched_main.c >> +++ b/drivers/gpu/drm/scheduler/sched_main.c >> @@ -857,7 +857,7 @@ void drm_sched_job_arm(struct drm_sched_job *job) >>       struct drm_gpu_scheduler *sched; >>       struct drm_sched_entity *entity = job->entity; >> -    BUG_ON(!entity); >> +    WARN_ON(!entity); >>       drm_sched_entity_select_rq(entity); > > void drm_sched_entity_select_rq(struct drm_sched_entity *entity) > { >     struct dma_fence *fence; >     struct drm_gpu_scheduler *sched; >     struct drm_sched_rq *rq; > >     /* single possible engine and already selected */ >     if (!entity->sched_list) > > Still the same end result. > > I believe best practice is to simply not have BUG_ON's followed by null Sorry I meant WARN_ONs. If we think there is scope for bad things to happen after letting the execution proceed then I would add an early return to the WARN_ON (_ONCE?). That probably means to push job as well. Regards, Tvrtko > pointer dereferences since they add no value. Ie. it should just be > removed and not replaced. > > Regards, > > Tvrtko > > Regards, > > Tvrtko > >>       sched = entity->rq->sched; >