linux-kernel - Re: [Nouveau] [PATCH v2 2/3] drm/nouveau: Fix runtime PM leak in nv50_disp_atomic

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Date:   Tue, 17 Jul 2018 13:31:24 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Lyude Paul <lyude@...hat.com>, nouveau@...ts.freedesktop.org,
        Archit Taneja <architt@...eaurora.org>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Ben Skeggs <bskeggs@...hat.com>
Subject: Re: [Nouveau] [PATCH v2 2/3] drm/nouveau: Fix runtime PM leak in
 nv50_disp_atomic_commit()

On Tue, Jul 17, 2018 at 09:33:52AM +0200, Lukas Wunner wrote:
> On Thu, Jul 12, 2018 at 01:02:53PM -0400, Lyude Paul wrote:
> > --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > @@ -1878,7 +1878,7 @@ nv50_disp_atomic_commit(struct drm_device *dev,
> >  		nv50_disp_atomic_commit_tail(state);
> >  
> >  	drm_for_each_crtc(crtc, dev) {
> > -		if (crtc->state->enable) {
> > +		if (crtc->state->active) {
> >  			if (!drm->have_disp_power_ref) {
> >  				drm->have_disp_power_ref = true;
> >  				return 0;
> 
> Somewhat tangential comment on this older patch, since you
> continue to dig around in the runtime PM area:
> 
> Whenever a crtc is activated or deactivated in nouveau, we iterate
> over all crtcs and acquire a runtime PM if a crtc is active and
> previously there was no active one, or we drop a ref if none is
> active and previously there was an active one.
> 
> For a while now I've been thinking that it would be more straightforward
> to acquire a ref whenever a crtc is activated and drop one when a crtc
> is deactivated, i.e. hold one ref for every active crtc.  That way the
> have_disp_power_ref variable as well as the iteration logic could be
> removed, leading to a simplification.  Just a suggestion anyway.

The current code looks somewhat busted anyway. First problem is that
it's accessing crtc->state without the appropriate locks held (unless
something always pulls in all crtcs to every commit?). Second issue
is that the rpm_put() is called without waiting for nonblocking commits
to have finished so it looks like you can currentlly remove the power
before the hardware has been properly shut down.

-- 
Ville Syrjälä
Intel