From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-102.mailbox.org (mout-p-102.mailbox.org [80.241.56.152]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9D1952DF144 for ; Tue, 2 Sep 2025 07:27:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.152 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756798060; cv=none; b=TWHxNjmxhcefQli27V+d4s8vuIt4CvpdBdwTpnv/8Dnwc8oETnvvhtSD9cSLHAJkSqJN0x8gQURbWna8Y5gnZuDlHiZsygdNIGCKW02h1LZttEyUwwnmo49OEw1uOBPgqn2T6NSvRioVIiLZftOD6pR+H2tD430SJzrHrKc+vK0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756798060; c=relaxed/simple; bh=7MM3ZadM3wSzyNk1K9rxHLxE789t1JMtbclB6YOLwbg=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=F1FMODFJGd10ydTTvS2GPATKpes12RXTZvpcBTl7D4Tmw3cX5Av07m89WcTqaNnoTA7bvPPQNy5JpfxYXZeaIkWGJ6U8yQbTwo0Q1gkpf0xPHWf6UL0uHWe2cpV9O30/m8T7N8dCys6sCfnUnUJsfBQBzFOnEc718cMYy5gs3SM= ARC-Authentication-Results:i=1; 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d=mailbox.org; s=mail20150812; t=1756798049; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yG8I1xuTHEhEIkmbynHckFwP9cXa9p2PM0q5O3/0wtg=; b=cQprZjxXkdXeulkN41CYFIAnkNH/Qp3/xIVXYGi/Dddld7LiwABAnVp+y1Dj0cxHUNZgtf RePcPQWbQmleFUPyg8Rn3rhjqJx81lFVLLjyBK97BPH9CbQ5y2Bg1XkVo5HnMTRSz63wq/ f5e0ecoOHeclDG2HCUrBEthyr2ADxK1DlXv319P1gUTRYR3cDIyoZ9yauIkAjljBco/JBV Z6GTe7BWIUZT2/7z5sxnPiuhLR2eO3LxooKIbs2NUz+WiSppJIgVbV2TLhHMpqV9RiZ4gJ KrJ1DtGp/B6PlbUNFBswKPIDvPr59R+wnWbkFsktF41aTFCIJSSUIBQj8sWAAw== Message-ID: Subject: Re: [PATCH v2] drm/sched: Fix racy access to drm_sched_entity.dependency From: Philipp Stanner Reply-To: phasta@kernel.org To: Pierre-Eric Pelloux-Prayer , Matthew Brost , Danilo Krummrich , Philipp Stanner , Christian =?ISO-8859-1?Q?K=F6nig?= , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Tvrtko Ursulin Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Date: Tue, 02 Sep 2025 09:27:24 +0200 In-Reply-To: <20250901124032.1955-1-pierre-eric.pelloux-prayer@amd.com> References: <20250901124032.1955-1-pierre-eric.pelloux-prayer@amd.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MBO-RS-META: m9kgt19mrt1xki6y19ipjzxmsq48bans X-MBO-RS-ID: e19ebd61c6c47cd73d7 On Mon, 2025-09-01 at 14:40 +0200, Pierre-Eric Pelloux-Prayer wrote: > The drm_sched_job_unschedulable trace point can access > entity->dependency after it was cleared by the callback > installed in drm_sched_entity_add_dependency_cb, causing: >=20 > BUG: kernel NULL pointer dereference, address: 0000000000000020 > [...] > Workqueue: comp_1.1.0 drm_sched_run_job_work [gpu_sched] > RIP: 0010:trace_event_raw_event_drm_sched_job_unschedulable+0x70/0xd0 [gp= u_sched] >=20 > To fix this we either need to keep a reference to the fence before > setting up the callbacks, or move the trace_drm_sched_job_unschedulable > calls into drm_sched_entity_add_dependency_cb where they can be > done earlier. >=20 > Fixes: 76d97c870f29 ("drm/sched: Trace dependencies for GPU jobs") >=20 > Signed-off-by: Pierre-Eric Pelloux-Prayer > Reviewed-by: Tvrtko Ursulin Applied to drm-misc-next Thx P. > --- > =C2=A0drivers/gpu/drm/scheduler/sched_entity.c | 11 +++++++---- > =C2=A01 file changed, 7 insertions(+), 4 deletions(-) >=20 > diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/s= cheduler/sched_entity.c > index 8867b95ab089..3d06f72531ba 100644 > --- a/drivers/gpu/drm/scheduler/sched_entity.c > +++ b/drivers/gpu/drm/scheduler/sched_entity.c > @@ -391,7 +391,8 @@ EXPORT_SYMBOL(drm_sched_entity_set_priority); > =C2=A0 * Add a callback to the current dependency of the entity to wake u= p the > =C2=A0 * scheduler when the entity becomes available. > =C2=A0 */ > -static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *= entity) > +static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *= entity, > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct drm_sched_job *sched_jo= b) > =C2=A0{ > =C2=A0 struct drm_gpu_scheduler *sched =3D entity->rq->sched; > =C2=A0 struct dma_fence *fence =3D entity->dependency; > @@ -421,6 +422,10 @@ static bool drm_sched_entity_add_dependency_cb(struc= t drm_sched_entity *entity) > =C2=A0 entity->dependency =3D fence; > =C2=A0 } > =C2=A0 > + if (trace_drm_sched_job_unschedulable_enabled() && > + =C2=A0=C2=A0=C2=A0 !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &entity->depe= ndency->flags)) > + trace_drm_sched_job_unschedulable(sched_job, entity->dependency); > + > =C2=A0 if (!dma_fence_add_callback(entity->dependency, &entity->cb, > =C2=A0 =C2=A0=C2=A0=C2=A0 drm_sched_entity_wakeup)) > =C2=A0 return true; > @@ -461,10 +466,8 @@ struct drm_sched_job *drm_sched_entity_pop_job(struc= t drm_sched_entity *entity) > =C2=A0 > =C2=A0 while ((entity->dependency =3D > =C2=A0 drm_sched_job_dependency(sched_job, entity))) { > - if (drm_sched_entity_add_dependency_cb(entity)) { > - trace_drm_sched_job_unschedulable(sched_job, entity->dependency); > + if (drm_sched_entity_add_dependency_cb(entity, sched_job)) > =C2=A0 return NULL; > - } > =C2=A0 } > =C2=A0 > =C2=A0 /* skip jobs from entity that marked guilty */