[Intel-gfx] [PATCH] drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist

[Chris Wilson]

Quoting Mika Kuoppala (2020-04-02 09:44:33)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > Since gen7 full-ppgtt uses nested vm references (the ppGTT is a slot
> > within the global GTT and so has a buried i915_ggtt) we may need to go
> > through a couple of RCU barriers before we have freed all the structs.
> >
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/gt/intel_ggtt.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > index 894d08e5a21f..cb31ed712db3 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > @@ -684,8 +684,9 @@ static void ggtt_cleanup_hw(struct i915_ggtt *ggtt)
> >  
> >       atomic_set(&ggtt->vm.open, 0);
> >  
> > -     rcu_barrier(); /* flush the RCU'ed__i915_vm_release */
> > -     flush_workqueue(ggtt->vm.i915->wq);
> > +     do { /* flush the RCU'ed__i915_vm_release */
> > +             rcu_barrier();
> > +     } while (flush_workqueue(ggtt->vm.i915->wq));
> 
> flush_workqueue returns void. you want flush_work?

Darnation. I see in i915_gem_drain_workqueue() we just did N passes :(
-Chris