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Tue, 30 Sep 2025 20:32:55 -0700 (PDT) Received: from cmpatel-home.hsd1.or.comcast.net ([2601:1c0:5780:9200:3746:506c:1567:3ec2]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-27ed66cf6e7sm174291535ad.2.2025.09.30.20.32.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Sep 2025 20:32:54 -0700 (PDT) From: Chintan Patel To: maarten.lankhorst@linux.intel.com, maxime.ripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, syzbot+147ba789658184f0ce04@syzkaller.appspotmail.com, Chintan Patel Subject: [PATCH] drm/vblank: downgrade vblank wait timeout from WARN to debug Date: Tue, 30 Sep 2025 20:32:12 -0700 Message-ID: <20251001033212.25423-1-chintanlike@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When wait_event_timeout() in drm_wait_one_vblank() times out, the current WARN can cause unnecessary kernel panics in environments with panic_on_warn set (e.g. CI, fuzzing). These timeouts can happen under scheduler pressure or from invalid userspace calls, so they are not always a kernel bug. Replace the WARN with drm_dbg_kms() messages that provide useful context (last and current vblank counters) without crashing the system. Developers can still enable drm.debug to diagnose genuine problems. Reported-by: syzbot+147ba789658184f0ce04@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D147ba789658184f0ce04 Tested-by: syzbot+147ba789658184f0ce04@syzkaller.appspotmail.com Signed-off-by: Chintan Patel --- drivers/gpu/drm/drm_vblank.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c index 46f59883183d..c8dd9d4be26c 100644 --- a/drivers/gpu/drm/drm_vblank.c +++ b/drivers/gpu/drm/drm_vblank.c @@ -1289,7 +1289,7 @@ void drm_wait_one_vblank(struct drm_device *dev, unsi= gned int pipe) { struct drm_vblank_crtc *vblank =3D drm_vblank_crtc(dev, pipe); int ret; - u64 last; + u64 last, curr; =20 if (drm_WARN_ON(dev, pipe >=3D dev->num_crtcs)) return; @@ -1305,7 +1305,20 @@ void drm_wait_one_vblank(struct drm_device *dev, uns= igned int pipe) last !=3D drm_vblank_count(dev, pipe), msecs_to_jiffies(100)); =20 - drm_WARN(dev, ret =3D=3D 0, "vblank wait timed out on crtc %i\n", pipe); + curr =3D drm_vblank_count(dev, pipe); + + if (ret =3D=3D 0) { + /* + * Avoid spamming WARNs for timeouts which can be caused by + * heavy scheduling pressure or invalid userspace calls (fuzzing). + * Use debug message instead. + */ + drm_dbg_kms(dev, "WAIT_VBLANK: timeout crtc=3D%d, last=3D%llu, curr=3D%l= lu\n", + pipe, last, curr); + } else { + drm_dbg_kms(dev, "WAIT_VBLANK: completed crtc=3D%d, last=3D%llu, curr=3D= %llu\n", + pipe, last, curr); + } =20 drm_vblank_put(dev, pipe); } --=20 2.43.0