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

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Date:   Thu, 25 Mar 2021 08:55:50 -0300
From:   Melissa Wen <melissa.srw@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...ux.ie>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        syzbot+4fc21a003c8332eb0bdd@...kaller.appspotmail.com,
        DRI <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/vkms: fix misuse of WARN_ON

On 03/25, Dmitry Vyukov wrote:
> On Wed, Mar 24, 2021 at 11:00 PM Melissa Wen <melissa.srw@...il.com> wrote:
> >
> > On 03/20, Dmitry Vyukov wrote:
> > > 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__);
> >
> > Hi Dmitry,
> >
> > Thanks for your patch.
> >
> > Looks good to me.
> > The Change-Id tag just seems a little noisy to me, but can be
> > fixed while applying.
> 
> Yes, please drop Change-Id when applying if possible. Sorry for that.
> Thanks for the review, Melissa.

Applied to drm-misc-next.

Thanks,

Melissa
> 
> > Acked-by: Melissa Wen <melissa.srw@...il.com>
> >
> > >
> > >       spin_lock(&output->lock);
> > >       ret = drm_crtc_handle_vblank(crtc);
> > >
> > > base-commit: e94c55b8e0a0bbe9a026250cf31e2fa45957d776
> > > --
> > > 2.31.0.291.g576ba9dcdaf-goog
> > >