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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
v1…v2: Rebase to v5.4-rc3
drivers/gpu/drm/i915/i915_request.c | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 1c5506822dc72..cf10246fb01ad 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -205,14 +205,14 @@ 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);
}
static bool i915_request_retire(struct i915_request *rq)
@@ -272,8 +272,6 @@ static bool i915_request_retire(struct i915_request *rq)
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_
@@ -282,7 +280,7 @@ static 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);
@@ -297,9 +295,7 @@ static 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);
--
2.23.0
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