Re: [PATCH 18/28] drm: avoid uninitialized timestamp use in wait_vblank

Daniel Vetter
2016-10-18T07:46:15Z

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@gmail.com>
> > Cc: Rob Clark <robdclark@gmail.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Signed-off-by: Arnd Bergmann <arnd@arndb.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@gmail.com>

Applied to drm-misc, thanks.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation