During request construction, we take the timeline->mutex to ensure
exclusive access to the ringbuffer (for command emission) and the
timeline itself (for command ordering). The timeline->mutex should not
be dropped by callers until we release it in i915_request_add().
lockdep provides a pin/unpin lock facility to detect accidental unlocks
inside critical sections, so put it to use for request construction.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_request.c | 5 +++++
drivers/gpu/drm/i915/i915_request.h | 10 ++++++++++
2 files changed, 15 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 82094b9f5ba7..7f8a4eba98b8 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -751,7 +751,10 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
rq->infix = rq->ring->emit; /* end of header; start of user payload */
/* Check that we didn't interrupt ourselves with a new request */
+ lockdep_assert_held(&rq->timeline->mutex);
GEM_BUG_ON(rq->timeline->seqno != rq->fence.seqno);
+ rq->cookie = lockdep_pin_lock(&rq->timeline->mutex);
+
return rq;
err_unwind:
@@ -1070,6 +1073,8 @@ void i915_request_add(struct i915_request *request)
engine->name, request->fence.context, request->fence.seqno);
lockdep_assert_held(&request->timeline->mutex);
+ lockdep_unpin_lock(&request->timeline->mutex, request->cookie);
+
trace_i915_request_add(request);
/*
diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
index cd6c130964cd..875be6f71412 100644
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -26,6 +26,7 @@
#define I915_REQUEST_H
#include <linux/dma-fence.h>
+#include <linux/lockdep.h>
#include "i915_gem.h"
#include "i915_scheduler.h"
@@ -120,6 +121,15 @@ struct i915_request {
*/
unsigned long rcustate;
+ /*
+ * We pin the timeline->mutex while constructing the request to
+ * ensure that no caller accidentally drops it during construction.
+ * The timeline->mutex must be held to ensure that only this caller
+ * can use the ring and manipulate the associated timeline during
+ * construction.
+ */
+ struct pin_cookie cookie;
+
/*
* Fences for the various phases in the request's lifetime.
*
--
2.20.1
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