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Wed, 1 Oct 2025 06:28:52 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id LpFeCiTK3GicCwAAD6G6ig (envelope-from ); Wed, 01 Oct 2025 06:28:52 +0000 Message-ID: <861c82b3-541b-4746-a5dd-88c614e92b16@suse.de> Date: Wed, 1 Oct 2025 08:28:51 +0200 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/vblank: downgrade vblank wait timeout from WARN to debug To: Chintan Patel , maarten.lankhorst@linux.intel.com, maxime.ripard@kernel.org, airlied@gmail.com, simona@ffwll.ch Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, syzbot+147ba789658184f0ce04@syzkaller.appspotmail.com References: <20251001033212.25423-1-chintanlike@gmail.com> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: <20251001033212.25423-1-chintanlike@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCPT_COUNT_SEVEN(0.00)[8]; FREEMAIL_TO(0.00)[gmail.com,linux.intel.com,kernel.org,ffwll.ch]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; TAGGED_RCPT(0.00)[147ba789658184f0ce04]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; TO_DN_SOME(0.00)[] X-Spam-Flag: NO X-Spam-Level: X-Spam-Score: -2.80 Hi Am 01.10.25 um 05:32 schrieb Chintan Patel: > 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=147ba789658184f0ce04 > 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, unsigned int pipe) > { > struct drm_vblank_crtc *vblank = drm_vblank_crtc(dev, pipe); > int ret; > - u64 last; > + u64 last, curr; > > if (drm_WARN_ON(dev, pipe >= dev->num_crtcs)) > return; > @@ -1305,7 +1305,20 @@ void drm_wait_one_vblank(struct drm_device *dev, unsigned int pipe) > last != drm_vblank_count(dev, pipe), > msecs_to_jiffies(100)); > > - drm_WARN(dev, ret == 0, "vblank wait timed out on crtc %i\n", pipe); > + curr = drm_vblank_count(dev, pipe); > + > + if (ret == 0) { if (!ret) > + /* > + * Avoid spamming WARNs for timeouts which can be caused by > + * heavy scheduling pressure or invalid userspace calls (fuzzing). > + * Use debug message instead. > + */ The comment is not necessary. The commit description gives a good rational. > + drm_dbg_kms(dev, "WAIT_VBLANK: timeout crtc=%d, last=%llu, curr=%llu\n", > + pipe, last, curr); > + } else { > + drm_dbg_kms(dev, "WAIT_VBLANK: completed crtc=%d, last=%llu, curr=%llu\n", > + pipe, last, curr); > + } Rather drop the else branch. Best regards Thomas > > drm_vblank_put(dev, pipe); > } -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)