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Subject: Re: [PATCH 18/28] drm: avoid uninitialized timestamp use in
 wait_vblank
To: Arnd Bergmann <arnd@arndb.de>, David Airlie <airlied@linux.ie>
References: <20161017220342.1627073-1-arnd@arndb.de>
 <20161017221355.1861551-6-arnd@arndb.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Rob Clark <robdclark@gmail.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Dave Airlie <airlied@redhat.com>,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Gustavo Padovan <gustavo.padovan@collabora.co.uk>,
        Matthew Auld <matthew.auld@intel.com>, dri-devel@lists.freedesktop.org
From: Mario Kleiner <mario.kleiner.de@gmail.com>
Message-ID: <374ecb85-dfff-ecc4-99ee-dba5ccbc169f@gmail.com>
Date: Tue, 18 Oct 2016 01:47:24 +0200
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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.
>
>  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>

-mario