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: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191017161352.e5z3ugse7gxl5ari@linutronix.de

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index f1cadad4e81cacfce23887098bf83e6c028f36a2..4575f368455d581589d594d6346efc6da6b7d83e 100644 (file)
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -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);