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

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Date:   Thu, 25 Mar 2021 07:48:32 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Melissa Wen <melissa.srw@...il.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 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.

> 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
> >