linux-kernel - [PATCH] drm/vkms: fix misuse of WARN

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Date:   Sat, 20 Mar 2021 14:28:40 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     daniel@...ll.ch, airlied@...ux.ie, hamohammed.sa@...il.com,
        melissa.srw@...il.com, rodrigosiqueiramelo@...il.com
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot+4fc21a003c8332eb0bdd@...kaller.appspotmail.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/vkms: fix misuse of WARN_ON

vkms_vblank_simulate() uses WARN_ON for timing-dependent condition
(timer overrun). This is a mis-use of WARN_ON, WARN_ON must be used
to denote kernel bugs. Use pr_warn() instead.

Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
Reported-by: syzbot+4fc21a003c8332eb0bdd@...kaller.appspotmail.com
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
Cc: Melissa Wen <melissa.srw@...il.com>
Cc: Haneen Mohammed <hamohammed.sa@...il.com>
Cc: Daniel Vetter <daniel@...ll.ch>
Cc: David Airlie <airlied@...ux.ie>
Cc: dri-devel@...ts.freedesktop.org
Cc: linux-kernel@...r.kernel.org
Change-Id: I7f01c288092bc7e472ec63af198f93ce3d8c49f7
---
 drivers/gpu/drm/vkms/vkms_crtc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
index 0443b7deeaef6..758d8a98d96b3 100644
--- a/drivers/gpu/drm/vkms/vkms_crtc.c
+++ b/drivers/gpu/drm/vkms/vkms_crtc.c
@@ -18,7 +18,8 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
 
 	ret_overrun = hrtimer_forward_now(&output->vblank_hrtimer,
 					  output->period_ns);
-	WARN_ON(ret_overrun != 1);
+	if (ret_overrun != 1)
+		pr_warn("%s: vblank timer overrun\n", __func__);
 
 	spin_lock(&output->lock);
 	ret = drm_crtc_handle_vblank(crtc);

base-commit: e94c55b8e0a0bbe9a026250cf31e2fa45957d776
-- 
2.31.0.291.g576ba9dcdaf-goog