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

Imre Deak
2014-04-23T07:52:42Z

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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>