linux-kernel - [PATCH 18/28] drm: avoid uninitialized timestamp use in wait

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Date:   Tue, 18 Oct 2016 00:13:39 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     David Airlie <airlied@...ux.ie>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Rob Clark <robdclark@...il.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Mario Kleiner <mario.kleiner.de@...il.com>,
        Dave Airlie <airlied@...hat.com>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Alex Deucher <alexander.deucher@....com>,
        Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
        Matthew Auld <matthew.auld@...el.com>,
        dri-devel@...ts.freedesktop.org
Subject: [PATCH 18/28] drm: avoid uninitialized timestamp use in wait_vblank

gcc warns about the timestamp in drm_wait_vblank being possibly
used without an initialization:

drivers/gpu/drm/drm_irq.c: In function 'drm_crtc_send_vblank_event':
drivers/gpu/drm/drm_irq.c:992:24: error: 'now.tv_usec' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/gpu/drm/drm_irq.c:1069:17: note: 'now.tv_usec' was declared here
drivers/gpu/drm/drm_irq.c:991:23: error: 'now.tv_sec' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This can happen if drm_vblank_count_and_time() returns 0 in its
error path. To sanitize the error case, I'm changing that function
to return a zero timestamp when it fails.

Fixes: e6ae8687a87b ("drm: idiot-proof vblank")
Reviewed-by: David Herrmann <dh.herrmann@...il.com>
Cc: Rob Clark <robdclark@...il.com>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
First submitted in January 2016, second submission in February,
the patch is still required.

 drivers/gpu/drm/drm_irq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index b969a64..48a6167 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -952,8 +952,10 @@ static u32 drm_vblank_count_and_time(struct drm_device *dev, unsigned int pipe,
 	u32 vblank_count;
 	unsigned int seq;
 
-	if (WARN_ON(pipe >= dev->num_crtcs))
+	if (WARN_ON(pipe >= dev->num_crtcs)) {
+		*vblanktime = (struct timeval) { 0 };
 		return 0;
+	}
 
 	do {
 		seq = read_seqbegin(&vblank->seqlock);
-- 
2.9.0