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

[Chris Wilson]

Quoting Chris Wilson (2020-04-02 09:48:18)
> 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 :(

Waitasec this is i915->wq, we can just use i915_gem_drain_workqueue()
(although that's now a misnomer).
-Chris