[PATCH 19/27] drm/i915: Push the i915_active.retire into a worker

[Chris Wilson]

As we need to use a mutex to serialisation i915_active activation
(because we want to allow the callback to sleep), we need to push the
i915_active.retire into a worker callback in case we get need to retire
from an atomic context.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_active.c       | 54 ++++++++++++++++++------
 drivers/gpu/drm/i915/i915_active_types.h |  3 ++
 2 files changed, 44 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index 6a9f8d37f415..f76a2b4ef95d 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -30,18 +30,14 @@ struct active_node {
 };
 
 static void
-active_retire(struct i915_active *ref)
+__active_retire(struct i915_active *ref)
 {
 	struct active_node *it, *n;
 	struct rb_root root;
 	bool retire = false;
 
-	GEM_BUG_ON(!atomic_read(&ref->count));
-	if (atomic_add_unless(&ref->count, -1, 1))
-		return;
-
-	/* One active may be flushed from inside the acquire of another */
-	mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING);
+	lockdep_assert_held(&ref->mutex);
+	GEM_BUG_ON(i915_active_is_idle(ref));
 
 	/* return the unused nodes to our slabcache -- flushing the allocator */
 	if (atomic_dec_and_test(&ref->count)) {
@@ -63,6 +59,35 @@ active_retire(struct i915_active *ref)
 	}
 }
 
+static void
+active_work(struct work_struct *wrk)
+{
+	struct i915_active *ref = container_of(wrk, typeof(*ref), work);
+
+	GEM_BUG_ON(!atomic_read(&ref->count));
+	if (atomic_add_unless(&ref->count, -1, 1))
+		return;
+
+	mutex_lock(&ref->mutex);
+	__active_retire(ref);
+}
+
+static void
+active_retire(struct i915_active *ref)
+{
+	GEM_BUG_ON(!atomic_read(&ref->count));
+	if (atomic_add_unless(&ref->count, -1, 1))
+		return;
+
+	/* If we are inside interrupt context (fence signaling), defer */
+	if (!mutex_trylock(&ref->mutex)) {
+		queue_work(system_unbound_wq, &ref->work);
+		return;
+	}
+
+	__active_retire(ref);
+}
+
 static void
 node_retire(struct i915_active_request *base, struct i915_request *rq)
 {
@@ -140,6 +165,7 @@ void __i915_active_init(struct drm_i915_private *i915,
 	init_llist_head(&ref->barriers);
 	atomic_set(&ref->count, 0);
 	__mutex_init(&ref->mutex, "i915_active", key);
+	INIT_WORK(&ref->work, active_work);
 }
 
 int i915_active_ref(struct i915_active *ref,
@@ -208,8 +234,10 @@ int i915_active_wait(struct i915_active *ref)
 	if (err)
 		return err;
 
-	if (!atomic_add_unless(&ref->count, 1, 0))
-		goto unlock;
+	if (!atomic_add_unless(&ref->count, 1, 0)) {
+		mutex_unlock(&ref->mutex);
+		return 0;
+	}
 
 	rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
 		err = i915_active_request_retire(&it->base, BKL(ref));
@@ -217,9 +245,8 @@ int i915_active_wait(struct i915_active *ref)
 			break;
 	}
 
-	active_retire(ref);
-unlock:
-	mutex_unlock(&ref->mutex);
+	__active_retire(ref);
+	flush_work(&ref->work);
 	return err;
 }
 
@@ -260,8 +287,9 @@ int i915_request_await_active(struct i915_request *rq, struct i915_active *ref)
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
 void i915_active_fini(struct i915_active *ref)
 {
-	GEM_BUG_ON(!RB_EMPTY_ROOT(&ref->tree));
 	GEM_BUG_ON(atomic_read(&ref->count));
+	GEM_BUG_ON(work_pending(&ref->work));
+	GEM_BUG_ON(!RB_EMPTY_ROOT(&ref->tree));
 	mutex_destroy(&ref->mutex);
 }
 #endif
diff --git a/drivers/gpu/drm/i915/i915_active_types.h b/drivers/gpu/drm/i915/i915_active_types.h
index 5b0a3024ce24..06acdffe0f6d 100644
--- a/drivers/gpu/drm/i915/i915_active_types.h
+++ b/drivers/gpu/drm/i915/i915_active_types.h
@@ -12,6 +12,7 @@
 #include <linux/mutex.h>
 #include <linux/rbtree.h>
 #include <linux/rcupdate.h>
+#include <linux/workqueue.h>
 
 struct drm_i915_private;
 struct i915_active_request;
@@ -39,6 +40,8 @@ struct i915_active {
 	int (*active)(struct i915_active *ref);
 	void (*retire)(struct i915_active *ref);
 
+	struct work_struct work;
+
 	struct llist_head barriers;
 };
 
-- 
2.20.1