Quoting Sebastian Andrzej Siewior (2019-10-10 17:06:40)
The locks (active.lock and rq->lock) need to be taken with disabled interrupts. This is done in i915_request_retire() by disabling the interrupts independently of the locks itself. While local_irq_disable()+spin_lock() equals spin_lock_irq() on vanilla it does not on PREEMPT_RT. Also, it is not obvious if there is a special reason to why the interrupts are disabled independently of the lock.
Enable/disable interrupts as part of the locking instruction.
Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de
drivers/gpu/drm/i915/i915_request.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
--- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -251,15 +251,13 @@ static bool i915_request_retire(struct i active->retire(active, rq); }
local_irq_disable();/* * We only loosely track inflight requests across preemption, * and so we may find ourselves attempting to retire a _completed_ * request that we have removed from the HW and put back on a run * queue. */spin_lock(&rq->engine->active.lock);
spin_lock_irq(&rq->engine->active.lock); list_del(&rq->sched.link); spin_unlock(&rq->engine->active.lock);@@ -278,9 +276,7 @@ static bool i915_request_retire(struct i __notify_execute_cb(rq); } GEM_BUG_ON(!list_empty(&rq->execute_cb));
spin_unlock(&rq->lock);local_irq_enable();
spin_unlock_irq(&rq->lock);
Nothing screams about the imbalance? irq off from one lock to the other? -Chris