drm/i915/guc: Release submit fence from an irq_work

A subsequent patch will flip the locking hierarchy from
ce->guc_state.lock -> sched_engine->lock to sched_engine->lock ->
ce->guc_state.lock. As such we need to release the submit fence for a
request from an IRQ to break a lock inversion - i.e. the fence must be
release went holding ce->guc_state.lock and the releasing of the can
acquire sched_engine->lock.

v2:
 (Daniele)
  - Delete request from list before calling irq_work_queue
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210909164744.31249-16-matthew.brost@intel.com

drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c

@@ -2049,17 +2049,32 @@ static const struct intel_context_ops guc_context_ops = {
 	.create_virtual = guc_create_virtual,
 };
 
+static void submit_work_cb(struct irq_work *wrk)
+{
+	struct i915_request *rq = container_of(wrk, typeof(*rq), submit_work);
+
+	might_lock(&rq->engine->sched_engine->lock);
+	i915_sw_fence_complete(&rq->submit);
+}
+
 static void __guc_signal_context_fence(struct intel_context *ce)
 {
-	struct i915_request *rq;
+	struct i915_request *rq, *rn;
 
 	lockdep_assert_held(&ce->guc_state.lock);
 
 	if (!list_empty(&ce->guc_state.fences))
 		trace_intel_context_fence_release(ce);
 
-	list_for_each_entry(rq, &ce->guc_state.fences, guc_fence_link)
-		i915_sw_fence_complete(&rq->submit);
+	/*
+	 * Use an IRQ to ensure locking order of sched_engine->lock ->
+	 * ce->guc_state.lock is preserved.
+	 */
+	list_for_each_entry_safe(rq, rn, &ce->guc_state.fences,
+				 guc_fence_link) {
+		list_del(&rq->guc_fence_link);
+		irq_work_queue(&rq->submit_work);
+	}
 
 	INIT_LIST_HEAD(&ce->guc_state.fences);
 }
@@ -2169,6 +2184,7 @@ static int guc_request_alloc(struct i915_request *rq)
 	spin_lock_irqsave(&ce->guc_state.lock, flags);
 	if (context_wait_for_deregister_to_register(ce) ||
 	    context_pending_disable(ce)) {
+		init_irq_work(&rq->submit_work, submit_work_cb);
 		i915_sw_fence_await(&rq->submit);
 
 		list_add_tail(&rq->guc_fence_link, &ce->guc_state.fences);

drivers/gpu/drm/i915/i915_request.h

@@ -218,6 +218,11 @@ struct i915_request {
 	};
 	struct llist_head execute_cb;
 	struct i915_sw_fence semaphore;
+	/**
+	 * @submit_work: complete submit fence from an IRQ if needed for
+	 * locking hierarchy reasons.
+	 */
+	struct irq_work submit_work;
 
 	/*
 	 * A list of everyone we wait upon, and everyone who waits upon us.