execlists_dequeue() is invoked from a function which uses local_irq_disable() to disable interrupts so the spin_lock() behaves like spin_lock_irq(). This breaks PREEMPT_RT because local_irq_disable() + spin_lock() is not the same as spin_lock_irq().
execlists_dequeue_irq() and execlists_dequeue() has each one caller only. If intel_engine_cs::active::lock is acquired and released with the _irq suffix then it behaves almost as if execlists_dequeue() would be invoked with disabled interrupts. The difference is the last part of the function which is then invoked with enabled interrupts. I can't tell if this makes a difference. From looking at it, it might work to move the last unlock at the end of the function as I didn't find anything that would acquire the lock again.
Reported-by: Clark Williams williams@redhat.com Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de --- .../drm/i915/gt/intel_execlists_submission.c | 17 +++++------------ 1 file changed, 5 insertions(+), 12 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c index fc77592d88a96..2ec1dd352960b 100644 --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c @@ -1265,7 +1265,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine) * and context switches) submission. */
- spin_lock(&engine->active.lock); + spin_lock_irq(&engine->active.lock);
/* * If the queue is higher priority than the last @@ -1365,7 +1365,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine) * Even if ELSP[1] is occupied and not worthy * of timeslices, our queue might be. */ - spin_unlock(&engine->active.lock); + spin_unlock_irq(&engine->active.lock); return; } } @@ -1391,7 +1391,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
if (last && !can_merge_rq(last, rq)) { spin_unlock(&ve->base.active.lock); - spin_unlock(&engine->active.lock); + spin_unlock_irq(&engine->active.lock); return; /* leave this for another sibling */ }
@@ -1552,7 +1552,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine) * interrupt for secondary ports). */ execlists->queue_priority_hint = queue_prio(execlists); - spin_unlock(&engine->active.lock); + spin_unlock_irq(&engine->active.lock);
/* * We can skip poking the HW if we ended up with exactly the same set @@ -1578,13 +1578,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine) } }
-static void execlists_dequeue_irq(struct intel_engine_cs *engine) -{ - local_irq_disable(); /* Suspend interrupts across request submission */ - execlists_dequeue(engine); - local_irq_enable(); /* flush irq_work (e.g. breadcrumb enabling) */ -} - static void clear_ports(struct i915_request **ports, int count) { memset_p((void **)ports, NULL, count); @@ -2377,7 +2370,7 @@ static void execlists_submission_tasklet(struct tasklet_struct *t) }
if (!engine->execlists.pending[0]) { - execlists_dequeue_irq(engine); + execlists_dequeue(engine); start_timeslice(engine); }