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

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Message-ID: <20161018074602.GY20761@phenom.ffwll.local>
Date:   Tue, 18 Oct 2016 09:46:02 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Mario Kleiner <mario.kleiner.de@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        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: Re: [PATCH 18/28] drm: avoid uninitialized timestamp use in
 wait_vblank

On Tue, Oct 18, 2016 at 01:47:24AM +0200, Mario Kleiner wrote:
> On 10/18/2016 12:13 AM, Arnd Bergmann wrote:
> > 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.

Hm, sorry I missed that.

> >  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);
> > 
> 
> Looks good to me.
> 
> Reviewed-by: Mario Kleiner <mario.kleiner.de@...il.com>

Applied to drm-misc, thanks.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch