Commit 1dfffa00 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Chris Wilson
Browse files

drm/i915: Don't disable interrupts independently of the lock 



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.
Chris Wilson confirmed that local_irq_disable() was just introduced as
an optimisation to avoid enabling/disabling interrupts during
lock/unlock combo.

Enable/disable interrupts as part of the locking instruction.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191017161352.e5z3ugse7gxl5ari@linutronix.de
parent e9768bfe

drivers/gpu/drm/i915/i915_request.c

+4 −8
Original line number Diff line number Diff line
@@ -206,14 +206,14 @@ static void remove_from_engine(struct i915_request *rq) 
	 * check that the rq still belongs to the newly locked engine.

	 */

	locked = READ_ONCE(rq->engine);

	spin_lock(&locked->active.lock);

	spin_lock_irq(&locked->active.lock);

	while (unlikely(locked != (engine = READ_ONCE(rq->engine)))) {

		spin_unlock(&locked->active.lock);

		spin_lock(&engine->active.lock);

		locked = engine;

	}

	list_del(&rq->sched.link);

	spin_unlock(&locked->active.lock);

	spin_unlock_irq(&locked->active.lock);

}



bool i915_request_retire(struct i915_request *rq)
@@ -242,8 +242,6 @@ bool i915_request_retire(struct i915_request *rq) 
				  &i915_request_timeline(rq)->requests));

	rq->ring->head = rq->postfix;



	local_irq_disable();



	/*

	 * We only loosely track inflight requests across preemption,

	 * and so we may find ourselves attempting to retire a _completed_
@@ -252,7 +250,7 @@ bool i915_request_retire(struct i915_request *rq) 
	 */

	remove_from_engine(rq);



	spin_lock(&rq->lock);

	spin_lock_irq(&rq->lock);

	i915_request_mark_complete(rq);

	if (!i915_request_signaled(rq))

		dma_fence_signal_locked(&rq->fence);
@@ -267,9 +265,7 @@ bool i915_request_retire(struct i915_request *rq) 
		__notify_execute_cb(rq);

	}

	GEM_BUG_ON(!list_empty(&rq->execute_cb));

	spin_unlock(&rq->lock);



	local_irq_enable();

	spin_unlock_irq(&rq->lock);



	remove_from_client(rq);

	list_del(&rq->link);

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