[PATCH 4/5] drm/exec, drm/xe: Avoid abusing the drm_exec retry pointer

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

The xe driver was using the drm_exec retry pointer directly to
restart the locking loop after out-of-memory errors. This is
relying on documented behaviour.

Instead add a drm_exec_retry() macro that can be used in this
situation, and that also asserts that the struct drm_exec is
in a state that is compatible with retrying:
Either newly initialized or in a contended state with all locks
dropped.

Use that macro in xe.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 drivers/gpu/drm/xe/xe_validation.h |  2 +-
 include/drm/drm_exec.h             | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_validation.h b/drivers/gpu/drm/xe/xe_validation.h
index a30e732c4d51..4cd955ce6cd2 100644
--- a/drivers/gpu/drm/xe/xe_validation.h
+++ b/drivers/gpu/drm/xe/xe_validation.h
@@ -146,7 +146,7 @@ bool xe_validation_should_retry(struct xe_validation_ctx *ctx, int *ret);
 #define xe_validation_retry_on_oom(_ctx, _ret)				\
 	do {								\
 		if (xe_validation_should_retry(_ctx, _ret))		\
-			goto *__drm_exec_retry_ptr;			\
+			drm_exec_retry((_ctx)->exec);			\
 	} while (0)
 
 /**
diff --git a/include/drm/drm_exec.h b/include/drm/drm_exec.h
index fc95a979e253..5ed5be1f8244 100644
--- a/include/drm/drm_exec.h
+++ b/include/drm/drm_exec.h
@@ -138,6 +138,19 @@ static inline bool drm_exec_is_contended(struct drm_exec *exec)
 	return !!exec->contended;
 }
 
+/**
+ * drm_exec_retry() - Unconditionally restart the loop to grab all locks.
+ * @exec: drm_exec object
+ *
+ * Unconditionally retry the loop to lock all objects. For consistency,
+ * the exec object needs to be newly initialized or contended.
+ */
+#define drm_exec_retry(_exec)				\
+	do {						\
+		WARN_ON(!drm_exec_is_contended(_exec)); \
+		goto *__drm_exec_retry_ptr;		\
+	} while (0)
+
 void drm_exec_init(struct drm_exec *exec, u32 flags, unsigned nr);
 void drm_exec_fini(struct drm_exec *exec);
 bool drm_exec_cleanup(struct drm_exec *exec);
-- 
2.53.0