[Intel-gfx] [PATCH 09/12] drm/i915/gt: Protect context lifetime with RCU

[Chris Wilson <chris@chris-wilson.co.uk>]

Allow a brief period for continued access to a dead intel_context by
deferring the release of the struct until after an RCU grace period.
As we are using a dedicated slab cache for the contexts, we can defer
the release of the slab pages via RCU, with the caveat that individual
structs may be reused from the freelist within an RCU grace period. To
handle that, we have to avoid clearing members of the zombie struct.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_context.c | 330 +++++++++++++-----------
 drivers/gpu/drm/i915/i915_active.c      |  10 +
 drivers/gpu/drm/i915/i915_active.h      |   2 +
 drivers/gpu/drm/i915/i915_utils.h       |   7 +
 4 files changed, 202 insertions(+), 147 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index 52db2bde44a3..4e7924640ffa 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -22,7 +22,7 @@ static struct i915_global_context {
 
 static struct intel_context *intel_context_alloc(void)
 {
-	return kmem_cache_zalloc(global.slab_ce, GFP_KERNEL);
+	return kmem_cache_alloc(global.slab_ce, GFP_KERNEL);
 }
 
 void intel_context_free(struct intel_context *ce)
@@ -30,6 +30,177 @@ void intel_context_free(struct intel_context *ce)
 	kmem_cache_free(global.slab_ce, ce);
 }
 
+static int __context_pin_state(struct i915_vma *vma)
+{
+	unsigned int bias = i915_ggtt_pin_bias(vma) | PIN_OFFSET_BIAS;
+	int err;
+
+	err = i915_ggtt_pin(vma, 0, bias | PIN_HIGH);
+	if (err)
+		return err;
+
+	err = i915_active_acquire(&vma->active);
+	if (err)
+		goto err_unpin;
+
+	/*
+	 * And mark it as a globally pinned object to let the shrinker know
+	 * it cannot reclaim the object until we release it.
+	 */
+	i915_vma_make_unshrinkable(vma);
+	vma->obj->mm.dirty = true;
+
+	return 0;
+
+err_unpin:
+	i915_vma_unpin(vma);
+	return err;
+}
+
+static void __context_unpin_state(struct i915_vma *vma)
+{
+	i915_vma_make_shrinkable(vma);
+	i915_active_release(&vma->active);
+	__i915_vma_unpin(vma);
+}
+
+static int __ring_active(struct intel_ring *ring)
+{
+	int err;
+
+	err = intel_ring_pin(ring);
+	if (err)
+		return err;
+
+	err = i915_active_acquire(&ring->vma->active);
+	if (err)
+		goto err_pin;
+
+	return 0;
+
+err_pin:
+	intel_ring_unpin(ring);
+	return err;
+}
+
+static void __ring_retire(struct intel_ring *ring)
+{
+	i915_active_release(&ring->vma->active);
+	intel_ring_unpin(ring);
+}
+
+__i915_active_call
+static void __intel_context_retire(struct i915_active *active)
+{
+	struct intel_context *ce = container_of(active, typeof(*ce), active);
+
+	CE_TRACE(ce, "retire runtime: { total:%lluns, avg:%lluns }\n",
+		 intel_context_get_total_runtime_ns(ce),
+		 intel_context_get_avg_runtime_ns(ce));
+
+	set_bit(CONTEXT_VALID_BIT, &ce->flags);
+	if (ce->state)
+		__context_unpin_state(ce->state);
+
+	intel_timeline_unpin(ce->timeline);
+	__ring_retire(ce->ring);
+
+	intel_context_put(ce);
+}
+
+static int __intel_context_active(struct i915_active *active)
+{
+	struct intel_context *ce = container_of(active, typeof(*ce), active);
+	int err;
+
+	CE_TRACE(ce, "active\n");
+
+	intel_context_get(ce);
+
+	err = __ring_active(ce->ring);
+	if (err)
+		goto err_put;
+
+	err = intel_timeline_pin(ce->timeline);
+	if (err)
+		goto err_ring;
+
+	if (!ce->state)
+		return 0;
+
+	err = __context_pin_state(ce->state);
+	if (err)
+		goto err_timeline;
+
+	return 0;
+
+err_timeline:
+	intel_timeline_unpin(ce->timeline);
+err_ring:
+	__ring_retire(ce->ring);
+err_put:
+	intel_context_put(ce);
+	return err;
+}
+
+static void __intel_context_ctor(void *arg)
+{
+	struct intel_context *ce = arg;
+
+	INIT_LIST_HEAD(&ce->signal_link);
+	INIT_LIST_HEAD(&ce->signals);
+
+	atomic_set(&ce->pin_count, 0);
+	mutex_init(&ce->pin_mutex);
+
+	ce->active_count = 0;
+	i915_active_init(&ce->active,
+			 __intel_context_active, __intel_context_retire);
+
+	ce->inflight = NULL;
+	ce->lrc_reg_state = NULL;
+	ce->lrc.desc = 0;
+}
+
+static void
+__intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
+{
+	GEM_BUG_ON(!engine->cops);
+	GEM_BUG_ON(!engine->gt->vm);
+
+	kref_init(&ce->ref);
+	i915_active_reinit(&ce->active);
+	mutex_reinit(&ce->pin_mutex);
+
+	ce->engine = engine;
+	ce->ops = engine->cops;
+	ce->sseu = engine->sseu;
+
+	ce->wa_bb_page = 0;
+	ce->flags = 0;
+	ce->tag = 0;
+
+	memset(&ce->runtime, 0, sizeof(ce->runtime));
+
+	ce->vm = i915_vm_get(engine->gt->vm);
+	ce->gem_context = NULL;
+
+	ce->ring = __intel_context_ring_size(SZ_4K);
+	ce->timeline = NULL;
+	ce->state = NULL;
+
+	GEM_BUG_ON(atomic_read(&ce->pin_count));
+	GEM_BUG_ON(ce->active_count);
+	GEM_BUG_ON(ce->inflight);
+}
+
+void
+intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
+{
+	__intel_context_ctor(ce);
+	__intel_context_init(ce, engine);
+}
+
 struct intel_context *
 intel_context_create(struct intel_engine_cs *engine)
 {
@@ -39,7 +210,7 @@ intel_context_create(struct intel_engine_cs *engine)
 	if (!ce)
 		return ERR_PTR(-ENOMEM);
 
-	intel_context_init(ce, engine);
+	__intel_context_init(ce, engine);
 	return ce;
 }
 
@@ -158,154 +329,13 @@ void intel_context_unpin(struct intel_context *ce)
 	/*
 	 * Once released, we may asynchronously drop the active reference.
 	 * As that may be the only reference keeping the context alive,
-	 * take an extra now so that it is not freed before we finish
+	 * hold onto RCU so that it is not freed before we finish
 	 * dereferencing it.
 	 */
-	intel_context_get(ce);
+	rcu_read_lock();
 	intel_context_active_release(ce);
-	intel_context_put(ce);
-}
-
-static int __context_pin_state(struct i915_vma *vma)
-{
-	unsigned int bias = i915_ggtt_pin_bias(vma) | PIN_OFFSET_BIAS;
-	int err;
-
-	err = i915_ggtt_pin(vma, 0, bias | PIN_HIGH);
-	if (err)
-		return err;
-
-	err = i915_active_acquire(&vma->active);
-	if (err)
-		goto err_unpin;
-
-	/*
-	 * And mark it as a globally pinned object to let the shrinker know
-	 * it cannot reclaim the object until we release it.
-	 */
-	i915_vma_make_unshrinkable(vma);
-	vma->obj->mm.dirty = true;
-
-	return 0;
-
-err_unpin:
-	i915_vma_unpin(vma);
-	return err;
-}
-
-static void __context_unpin_state(struct i915_vma *vma)
-{
-	i915_vma_make_shrinkable(vma);
-	i915_active_release(&vma->active);
-	__i915_vma_unpin(vma);
-}
-
-static int __ring_active(struct intel_ring *ring)
-{
-	int err;
-
-	err = intel_ring_pin(ring);
-	if (err)
-		return err;
-
-	err = i915_active_acquire(&ring->vma->active);
-	if (err)
-		goto err_pin;
-
-	return 0;
-
-err_pin:
-	intel_ring_unpin(ring);
-	return err;
-}
-
-static void __ring_retire(struct intel_ring *ring)
-{
-	i915_active_release(&ring->vma->active);
-	intel_ring_unpin(ring);
+	rcu_read_unlock();
 }
-
-__i915_active_call
-static void __intel_context_retire(struct i915_active *active)
-{
-	struct intel_context *ce = container_of(active, typeof(*ce), active);
-
-	CE_TRACE(ce, "retire runtime: { total:%lluns, avg:%lluns }\n",
-		 intel_context_get_total_runtime_ns(ce),
-		 intel_context_get_avg_runtime_ns(ce));
-
-	set_bit(CONTEXT_VALID_BIT, &ce->flags);
-	if (ce->state)
-		__context_unpin_state(ce->state);
-
-	intel_timeline_unpin(ce->timeline);
-	__ring_retire(ce->ring);
-
-	intel_context_put(ce);
-}
-
-static int __intel_context_active(struct i915_active *active)
-{
-	struct intel_context *ce = container_of(active, typeof(*ce), active);
-	int err;
-
-	CE_TRACE(ce, "active\n");
-
-	intel_context_get(ce);
-
-	err = __ring_active(ce->ring);
-	if (err)
-		goto err_put;
-
-	err = intel_timeline_pin(ce->timeline);
-	if (err)
-		goto err_ring;
-
-	if (!ce->state)
-		return 0;
-
-	err = __context_pin_state(ce->state);
-	if (err)
-		goto err_timeline;
-
-	return 0;
-
-err_timeline:
-	intel_timeline_unpin(ce->timeline);
-err_ring:
-	__ring_retire(ce->ring);
-err_put:
-	intel_context_put(ce);
-	return err;
-}
-
-void
-intel_context_init(struct intel_context *ce,
-		   struct intel_engine_cs *engine)
-{
-	GEM_BUG_ON(!engine->cops);
-	GEM_BUG_ON(!engine->gt->vm);
-
-	kref_init(&ce->ref);
-
-	ce->engine = engine;
-	ce->ops = engine->cops;
-	ce->sseu = engine->sseu;
-	ce->ring = __intel_context_ring_size(SZ_4K);
-
-	ewma_runtime_init(&ce->runtime.avg);
-
-	ce->vm = i915_vm_get(engine->gt->vm);
-
-	INIT_LIST_HEAD(&ce->signal_link);
-	INIT_LIST_HEAD(&ce->signals);
-
-	mutex_init(&ce->pin_mutex);
-
-	i915_active_init(&ce->active,
-			 __intel_context_active, __intel_context_retire);
-}
-
 void intel_context_fini(struct intel_context *ce)
 {
 	if (ce->timeline)
@@ -333,7 +363,13 @@ static struct i915_global_context global = { {
 
 int __init i915_global_context_init(void)
 {
-	global.slab_ce = KMEM_CACHE(intel_context, SLAB_HWCACHE_ALIGN);
+	global.slab_ce =
+		kmem_cache_create("intel_context",
+				  sizeof(struct intel_context),
+				  __alignof__(struct intel_context),
+				  SLAB_HWCACHE_ALIGN |
+				  SLAB_TYPESAFE_BY_RCU,
+				  __intel_context_ctor);
 	if (!global.slab_ce)
 		return -ENOMEM;
 
diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index d960d0be5bd2..adec6740b1ff 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -662,6 +662,16 @@ void i915_active_fini(struct i915_active *ref)
 }
 #endif
 
+void i915_active_reinit(struct i915_active *ref)
+{
+	GEM_BUG_ON(!i915_active_is_idle(ref));
+	debug_active_init(ref);
+	mutex_reinit(&ref->mutex);
+
+	ref->cache = NULL;
+	ref->tree = RB_ROOT;
+}
+
 static inline bool is_idle_barrier(struct active_node *node, u64 idx)
 {
 	return node->timeline == idx && !i915_active_fence_isset(&node->base);
diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
index cf4058150966..e0c2f13ac53c 100644
--- a/drivers/gpu/drm/i915/i915_active.h
+++ b/drivers/gpu/drm/i915/i915_active.h
@@ -219,6 +219,8 @@ void i915_active_fini(struct i915_active *ref);
 static inline void i915_active_fini(struct i915_active *ref) { }
 #endif
 
+void i915_active_reinit(struct i915_active *ref);
+
 int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
 					    struct intel_engine_cs *engine);
 void i915_active_acquire_barrier(struct i915_active *ref);
diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index 54773371e6bd..ef8db3aa75c7 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -443,6 +443,13 @@ static inline bool timer_expired(const struct timer_list *t)
 	return READ_ONCE(t->expires) && !timer_pending(t);
 }
 
+static inline void mutex_reinit(struct mutex *lock)
+{
+#if IS_ENABLED(CONFIG_DEBUG_MUTEXES)
+	lock->magic = lock;
+#endif
+}
+
 /*
  * This is a lookalike for IS_ENABLED() that takes a kconfig value,
  * e.g. CONFIG_DRM_I915_SPIN_REQUEST, and evaluates whether it is non-zero
-- 
2.20.1

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