Re: [PATCH v4] drm/i915: get a runtime PM ref for the deferred GPU reset work

[Imre Deak <imre.deak@intel.com>]

On Wed, 2014-04-23 at 09:07 +0200, Daniel Vetter wrote:
> On Wed, Apr 23, 2014 at 01:13:40AM +0300, Imre Deak wrote:
> > Atm we can end up in the GPU reset deferred work in D3 state if the last
> > runtime PM reference is dropped between detecting a hang/scheduling the
> > work and executing the work. At least one such case I could trigger is
> > the simulated reset via the i915_wedged debugfs entry. Fix this by
> > getting an RPM reference around accessing the HW in the reset work.
> > 
> > v2:
> > - Instead of getting/putting the RPM reference in the reset work itself,
> >   get it already before scheduling the work. By this we also prevent
> >   going to D3 before the work gets to run, in addition to making sure
> >   that we run the work itself in D0. (Ville, Daniel)
> > v3:
> > - fix inverted logic fail when putting the RPM ref on behalf of a
> >   cancelled GPU reset work (Ville)
> > v4:
> > - Taking the RPM ref in the interrupt handler isn't really needed b/c
> >   it's already guaranteed that we hold an RPM ref until the end of the
> >   reset work in all cases we care about. So take the ref in the reset
> >   work (for cases like i915_wedged_set). (Daniel)
> > 
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_irq.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index a651d0d..0e47111 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -2175,6 +2175,14 @@ static void i915_error_work_func(struct work_struct *work)
> >  				   reset_event);
> >  
> >  		/*
> > +		 * In most cases it's guaranteed that we get here with an RPM
> > +		 * reference held, for example because there is a pending GPU
> > +		 * request that won't finish until the reset is done. This
> > +		 * isn't the case at least when we get here by doing a
> > +		 * simulated reset via debugs, so get an RPM reference.
> 
>                                       ^debugfs
> 
> Also maybe "..., so get a RPM reference just to quiet the warnings."

Do you mean it's not a problem to perform the reset in D3 state other
than getting warnings?

--Imre

> -Daniel
> 
> > +		 */
> > +		intel_runtime_pm_get(dev_priv);
> > +		/*
> >  		 * All state reset _must_ be completed before we update the
> >  		 * reset counter, for otherwise waiters might miss the reset
> >  		 * pending state and not properly drop locks, resulting in
> > @@ -2184,6 +2192,8 @@ static void i915_error_work_func(struct work_struct *work)
> >  
> >  		intel_display_handle_reset(dev);
> >  
> > +		intel_runtime_pm_put(dev_priv);
> > +
> >  		if (ret == 0) {
> >  			/*
> >  			 * After all the gem state is reset, increment the reset
> > -- 
> > 1.8.4
> > 
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