Quoting Mika Kuoppala (2020-01-29 09:29:43)
> Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
>
> > We write to execlists->pending[0] in process_csb() to acknowledge the
> > completion of the ESLP update, outside of the main spinlock. When we
> > check the current status of the previous submission in
> > __execlists_submission_tasklet() we should therefore use READ_ONCE() to
> > reflect and document the unsynchronized read.
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gt/intel_lrc.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > index cf6c43bd540a..058484958e87 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > @@ -2347,7 +2347,7 @@ static void process_csb(struct intel_engine_cs *engine)
> > static void __execlists_submission_tasklet(struct intel_engine_cs *const engine)
> > {
> > lockdep_assert_held(&engine->active.lock);
> > - if (!engine->execlists.pending[0]) {
> > + if (!READ_ONCE(engine->execlists.pending[0])) {
>
> With same token, should we also include assert_pending_invalid()
> read of pending with READ_ONCE?
That happens on the control paths, so the state of pending[] at that
point should be static (and the compiler can be left to its own
devices).
-Chris
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