On 18/03/2019 09:51, Chris Wilson wrote:
As the final request on a ring may hold the reference to this ring (via
retiring the last pinned context), we may find ourselves chasing a
dangling pointer on completion of the list.
A quick solution is to hold a reference to the ring itself as we retire
along it so that we only free it after we stop dereferencing it.
Is there a guilty commit to reference as Fixes: ?
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_request.c | 6 +++++-
drivers/gpu/drm/i915/intel_engine_types.h | 2 ++
drivers/gpu/drm/i915/intel_lrc.c | 4 ++--
drivers/gpu/drm/i915/intel_ringbuffer.c | 9 +++++----
drivers/gpu/drm/i915/intel_ringbuffer.h | 13 ++++++++++++-
drivers/gpu/drm/i915/selftests/mock_engine.c | 1 +
6 files changed, 27 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 9533a85cb0b3..0a3d94517d0a 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1332,8 +1332,12 @@ void i915_retire_requests(struct drm_i915_private *i915)
if (!i915->gt.active_requests)
return;
- list_for_each_entry_safe(ring, tmp, &i915->gt.active_rings, active_link)
+ list_for_each_entry_safe(ring, tmp,
+ &i915->gt.active_rings, active_link) {
+ intel_ring_get(ring); /* last rq holds reference! */
ring_retire_requests(ring);
+ intel_ring_put(ring);
+ }
Where does it chase a dangling pointer? It used the safe iterator already.
}
#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
diff --git a/drivers/gpu/drm/i915/intel_engine_types.h b/drivers/gpu/drm/i915/intel_engine_types.h
index 79a166b9a81b..549fdfca17aa 100644
--- a/drivers/gpu/drm/i915/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/intel_engine_types.h
@@ -9,6 +9,7 @@
#include <linux/hashtable.h>
#include <linux/irq_work.h>
+#include <linux/kref.h>
#include <linux/list.h>
#include <linux/types.h>
@@ -58,6 +59,7 @@ struct intel_engine_hangcheck {
};
struct intel_ring {
+ struct kref ref;
struct i915_vma *vma;
void *vaddr;
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index aa50f03ba812..d3f1fe06d013 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1236,7 +1236,7 @@ static void execlists_submit_request(struct i915_request *request)
static void __execlists_context_fini(struct intel_context *ce)
{
- intel_ring_free(ce->ring);
+ intel_ring_put(ce->ring);
GEM_BUG_ON(i915_gem_object_is_active(ce->state->obj));
i915_gem_object_put(ce->state->obj);
@@ -2867,7 +2867,7 @@ static int execlists_context_deferred_alloc(struct intel_context *ce,
return 0;
error_ring_free:
- intel_ring_free(ring);
+ intel_ring_put(ring);
error_deref_obj:
i915_gem_object_put(ctx_obj);
return ret;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 746fe570466c..45a54fadc482 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1302,6 +1302,7 @@ intel_engine_create_ring(struct intel_engine_cs *engine,
if (!ring)
return ERR_PTR(-ENOMEM);
+ kref_init(&ring->ref);
INIT_LIST_HEAD(&ring->request_list);
ring->timeline = i915_timeline_get(timeline);
@@ -1326,9 +1327,9 @@ intel_engine_create_ring(struct intel_engine_cs *engine,
return ring;
}
-void
-intel_ring_free(struct intel_ring *ring)
+void intel_ring_free(struct kref *ref)
{
+ struct intel_ring *ring = container_of(ref, typeof(*ring), ref);
struct drm_i915_gem_object *obj = ring->vma->obj;
i915_vma_close(ring->vma);
@@ -1571,7 +1572,7 @@ static int intel_init_ring_buffer(struct intel_engine_cs *engine)
err_unpin:
intel_ring_unpin(ring);
err_ring:
- intel_ring_free(ring);
+ intel_ring_put(ring);
err:
intel_engine_cleanup_common(engine);
return err;
@@ -1585,7 +1586,7 @@ void intel_engine_cleanup(struct intel_engine_cs *engine)
(I915_READ_MODE(engine) & MODE_IDLE) == 0);
intel_ring_unpin(engine->buffer);
- intel_ring_free(engine->buffer);
+ intel_ring_put(engine->buffer);
if (engine->cleanup)
engine->cleanup(engine);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index e612bdca9fd9..a57489fcb302 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -231,7 +231,18 @@ int intel_ring_pin(struct intel_ring *ring);
void intel_ring_reset(struct intel_ring *ring, u32 tail);
unsigned int intel_ring_update_space(struct intel_ring *ring);
void intel_ring_unpin(struct intel_ring *ring);
-void intel_ring_free(struct intel_ring *ring);
+void intel_ring_free(struct kref *ref);
+
+static inline struct intel_ring *intel_ring_get(struct intel_ring *ring)
+{
+ kref_get(&ring->ref);
+ return ring;
+}
+
+static inline void intel_ring_put(struct intel_ring *ring)
+{
+ kref_put(&ring->ref, intel_ring_free);
+}
void intel_engine_stop(struct intel_engine_cs *engine);
void intel_engine_cleanup(struct intel_engine_cs *engine);
diff --git a/drivers/gpu/drm/i915/selftests/mock_engine.c b/drivers/gpu/drm/i915/selftests/mock_engine.c
index f6d120e05ee4..881450c694e9 100644
--- a/drivers/gpu/drm/i915/selftests/mock_engine.c
+++ b/drivers/gpu/drm/i915/selftests/mock_engine.c
@@ -57,6 +57,7 @@ static struct intel_ring *mock_ring(struct intel_engine_cs *engine)
return NULL;
}
+ kref_init(&ring->base.ref);
ring->base.size = sz;
ring->base.effective_size = sz;
ring->base.vaddr = (void *)(ring + 1);
Regards,
Tvrtko
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