[PATCH v2] drm/i915/gt: Ensure irqs' status does not change with spin_unlock

[Krzysztof Karas]

spin_unlock() function enables irqs regardless of their state
before spin_lock() was called. This might result in an interrupt
while holding a lock further down in the execution, as seen in
GitLab issue #13399.

Try to remedy the problem by saving irq state before spin lock
acquisition.

v2: add irqs' state save/restore calls to all locks/unlocks in
 signal_irq_work() execution (Maciej)

Signed-off-by: Krzysztof Karas <krzysztof.karas at intel.com>
---
This issue is hit rarely on CI and I was not able to reproduce
it locally. There might be more places where we should save and
restore irq state, so I am not adding "Closes" label for the
issue yet.

 drivers/gpu/drm/i915/gt/intel_breadcrumbs.c   | 21 ++++++++++++-------
 .../gpu/drm/i915/gt/uc/intel_guc_submission.c |  5 +++--
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index cc866773ba6f..dd5542726b41 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -53,13 +53,15 @@ static void __intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
 
 static void intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
 {
+	unsigned long flags;
+
 	if (!b->irq_engine)
 		return;
 
-	spin_lock(&b->irq_lock);
+	spin_lock_irqsave(&b->irq_lock, flags);
 	if (!b->irq_armed)
 		__intel_breadcrumbs_arm_irq(b);
-	spin_unlock(&b->irq_lock);
+	spin_unlock_irqrestore(&b->irq_lock, flags);
 }
 
 static void __intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
@@ -76,10 +78,12 @@ static void __intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
 
 static void intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
 {
-	spin_lock(&b->irq_lock);
+	unsigned long flags;
+
+	spin_lock_irqsave(&b->irq_lock, flags);
 	if (b->irq_armed)
 		__intel_breadcrumbs_disarm_irq(b);
-	spin_unlock(&b->irq_lock);
+	spin_unlock_irqrestore(&b->irq_lock, flags);
 }
 
 static void add_signaling_context(struct intel_breadcrumbs *b,
@@ -173,6 +177,7 @@ static void signal_irq_work(struct irq_work *work)
 	const ktime_t timestamp = ktime_get();
 	struct llist_node *signal, *sn;
 	struct intel_context *ce;
+	unsigned long flags;
 
 	signal = NULL;
 	if (unlikely(!llist_empty(&b->signaled_requests)))
@@ -226,10 +231,10 @@ static void signal_irq_work(struct irq_work *work)
 			 * spinlock as the callback chain may end up adding
 			 * more signalers to the same context or engine.
 			 */
-			spin_lock(&ce->signal_lock);
+			spin_lock_irqsave(&ce->signal_lock, flags);
 			list_del_rcu(&rq->signal_link);
 			release = remove_signaling_context(b, ce);
-			spin_unlock(&ce->signal_lock);
+			spin_unlock_irqrestore(&ce->signal_lock, flags);
 			if (release) {
 				if (intel_timeline_is_last(ce->timeline, rq))
 					add_retire(b, ce->timeline);
@@ -254,11 +259,11 @@ static void signal_irq_work(struct irq_work *work)
 		if (rq->engine->sched_engine->retire_inflight_request_prio)
 			rq->engine->sched_engine->retire_inflight_request_prio(rq);
 
-		spin_lock(&rq->lock);
+		spin_lock_irqsave(&rq->lock, flags);
 		list_replace(&rq->fence.cb_list, &cb_list);
 		__dma_fence_signal__timestamp(&rq->fence, timestamp);
 		__dma_fence_signal__notify(&rq->fence, &cb_list);
-		spin_unlock(&rq->lock);
+		spin_unlock_irqrestore(&rq->lock, flags);
 
 		i915_request_put(rq);
 	}
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 12f1ba7ca9c1..e9102f7246f5 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -4338,10 +4338,11 @@ static void guc_bump_inflight_request_prio(struct i915_request *rq,
 static void guc_retire_inflight_request_prio(struct i915_request *rq)
 {
 	struct intel_context *ce = request_to_scheduling_context(rq);
+	unsigned long flags;
 
-	spin_lock(&ce->guc_state.lock);
+	spin_lock_irqsave(&ce->guc_state.lock, flags);
 	guc_prio_fini(rq, ce);
-	spin_unlock(&ce->guc_state.lock);
+	spin_unlock_irqrestore(&ce->guc_state.lock, flags);
 }
 
 static void sanitize_hwsp(struct intel_engine_cs *engine)
-- 
2.34.1