On Fri, Dec 10, 2021 at 05:07:12PM -0800, John Harrison wrote:
> On 12/10/2021 16:56, Matthew Brost wrote:
> > From: John Harrison <John.C.Harrison@xxxxxxxxx>
> >
> > While attempting to debug a CT deadlock issue in various CI failures
> > (most easily reproduced with gem_ctx_create/basic-files), I was seeing
> > CPU deadlock errors being reported. This were because the context
> > destroy loop was blocking waiting on H2G space from inside an IRQ
> > spinlock. There was deadlock as such, it's just that the H2G queue was
> There was *no* deadlock as such
>
Let's fix this up when applying the series.
With that:
Reviewed-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> John.
>
> > full of context destroy commands and GuC was taking a long time to
> > process them. However, the kernel was seeing the large amount of time
> > spent inside the IRQ lock as a dead CPU. Various Bad Things(tm) would
> > then happen (heartbeat failures, CT deadlock errors, outstanding H2G
> > WARNs, etc.).
> >
> > Re-working the loop to only acquire the spinlock around the list
> > management (which is all it is meant to protect) rather than the
> > entire destroy operation seems to fix all the above issues.
> >
> > Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
> > ---
> > .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 45 ++++++++++++-------
> > 1 file changed, 28 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > index 36c2965db49b..96fcf869e3ff 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -2644,7 +2644,6 @@ static inline void guc_lrc_desc_unpin(struct intel_context *ce)
> > unsigned long flags;
> > bool disabled;
> > - lockdep_assert_held(&guc->submission_state.lock);
> > GEM_BUG_ON(!intel_gt_pm_is_awake(gt));
> > GEM_BUG_ON(!lrc_desc_registered(guc, ce->guc_id.id));
> > GEM_BUG_ON(ce != __get_context(guc, ce->guc_id.id));
> > @@ -2660,7 +2659,7 @@ static inline void guc_lrc_desc_unpin(struct intel_context *ce)
> > }
> > spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> > if (unlikely(disabled)) {
> > - __release_guc_id(guc, ce);
> > + release_guc_id(guc, ce);
> > __guc_context_destroy(ce);
> > return;
> > }
> > @@ -2694,36 +2693,48 @@ static void __guc_context_destroy(struct intel_context *ce)
> > static void guc_flush_destroyed_contexts(struct intel_guc *guc)
> > {
> > - struct intel_context *ce, *cn;
> > + struct intel_context *ce;
> > unsigned long flags;
> > GEM_BUG_ON(!submission_disabled(guc) &&
> > guc_submission_initialized(guc));
> > - spin_lock_irqsave(&guc->submission_state.lock, flags);
> > - list_for_each_entry_safe(ce, cn,
> > - &guc->submission_state.destroyed_contexts,
> > - destroyed_link) {
> > - list_del_init(&ce->destroyed_link);
> > - __release_guc_id(guc, ce);
> > + while (!list_empty(&guc->submission_state.destroyed_contexts)) {
> > + spin_lock_irqsave(&guc->submission_state.lock, flags);
> > + ce = list_first_entry_or_null(&guc->submission_state.destroyed_contexts,
> > + struct intel_context,
> > + destroyed_link);
> > + if (ce)
> > + list_del_init(&ce->destroyed_link);
> > + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> > +
> > + if (!ce)
> > + break;
> > +
> > + release_guc_id(guc, ce);
> > __guc_context_destroy(ce);
> > }
> > - spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> > }
> > static void deregister_destroyed_contexts(struct intel_guc *guc)
> > {
> > - struct intel_context *ce, *cn;
> > + struct intel_context *ce;
> > unsigned long flags;
> > - spin_lock_irqsave(&guc->submission_state.lock, flags);
> > - list_for_each_entry_safe(ce, cn,
> > - &guc->submission_state.destroyed_contexts,
> > - destroyed_link) {
> > - list_del_init(&ce->destroyed_link);
> > + while (!list_empty(&guc->submission_state.destroyed_contexts)) {
> > + spin_lock_irqsave(&guc->submission_state.lock, flags);
> > + ce = list_first_entry_or_null(&guc->submission_state.destroyed_contexts,
> > + struct intel_context,
> > + destroyed_link);
> > + if (ce)
> > + list_del_init(&ce->destroyed_link);
> > + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> > +
> > + if (!ce)
> > + break;
> > +
> > guc_lrc_desc_unpin(ce);
> > }
> > - spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> > }
> > static void destroyed_worker_func(struct work_struct *w)
>
