[igt-dev] [PATCH i-g-t] lib: Fix intel_get_current_physical_engine() iterator

[Chris Wilson]

If we run out of engines, intel_get_current_physical_engine() degrades
into an infinite loop as although it advanced the iterator, it did not
update its local engine pointer.

Reported-by: Petri Latvala <petri.latvala at intel.com>
Fixes: 17c77e7b0c3c ("lib/i915: add gem_engine_topology library and for_each loop definition")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Andi Shyti <andi.shyti at intel.com>
Cc: Petri Latvala <petri.latvala at intel.com>
---
 lib/i915/gem_engine_topology.c | 49 +++++-----------------------------
 lib/i915/gem_engine_topology.h | 36 ++++++++++++++++---------
 2 files changed, 29 insertions(+), 56 deletions(-)

diff --git a/lib/i915/gem_engine_topology.c b/lib/i915/gem_engine_topology.c
index fdd1b9516..17f67786f 100644
--- a/lib/i915/gem_engine_topology.c
+++ b/lib/i915/gem_engine_topology.c
@@ -81,11 +81,10 @@ static void ctx_map_engines(int fd, struct intel_engine_data *ed,
 			    struct drm_i915_gem_context_param *param)
 {
 	struct i915_context_param_engines *engines =
-			from_user_pointer(param->value);
+		from_user_pointer(param->value);
 	int i = 0;
 
-	for (typeof(engines->engines[0]) *p =
-	     &engines->engines[0];
+	for (struct i915_engine_class_instance *p = &engines->engines[0];
 	     i < ed->nengines; i++, p++) {
 		p->engine_class = ed->engines[i].class;
 		p->engine_instance = ed->engines[i].instance;
@@ -136,7 +135,7 @@ static void query_engine_list(int fd, struct intel_engine_data *ed)
 {
 	uint8_t buff[SIZEOF_QUERY] = { };
 	struct drm_i915_query_engine_info *query_engine =
-			(struct drm_i915_query_engine_info *) buff;
+		(struct drm_i915_query_engine_info *)buff;
 	int i;
 
 	query_engines(fd, query_engine, SIZEOF_QUERY);
@@ -149,41 +148,6 @@ static void query_engine_list(int fd, struct intel_engine_data *ed)
 	ed->nengines = query_engine->num_engines;
 }
 
-struct intel_execution_engine2 *
-intel_get_current_engine(struct intel_engine_data *ed)
-{
-	if (!ed->n)
-		ed->current_engine = &ed->engines[0];
-	else if (ed->n >= ed->nengines)
-		ed->current_engine = NULL;
-
-	return ed->current_engine;
-}
-
-void intel_next_engine(struct intel_engine_data *ed)
-{
-	if (ed->n + 1 < ed->nengines) {
-		ed->n++;
-		ed->current_engine = &ed->engines[ed->n];
-	} else {
-		ed->n = ed->nengines;
-		ed->current_engine = NULL;
-	}
-}
-
-struct intel_execution_engine2 *
-intel_get_current_physical_engine(struct intel_engine_data *ed)
-{
-	struct intel_execution_engine2 *e;
-
-	for (e = intel_get_current_engine(ed);
-	     e && e->is_virtual;
-	     intel_next_engine(ed))
-		;
-
-	return e;
-}
-
 static int gem_topology_get_param(int fd,
 				  struct drm_i915_gem_context_param *p)
 {
@@ -197,10 +161,9 @@ static int gem_topology_get_param(int fd,
 		return 0;
 
 	/* size will store the engine count */
-	p->size = (p->size - sizeof(struct i915_context_param_engines)) /
-		  (offsetof(struct i915_context_param_engines,
-			    engines[1]) -
-		  sizeof(struct i915_context_param_engines));
+	igt_assert(p->size >= sizeof(struct i915_context_param_engines));
+	p->size -= sizeof(struct i915_context_param_engines);
+	p->size /= sizeof(struct i915_engine_class_instance);
 
 	igt_assert_f(p->size <= GEM_MAX_ENGINES, "unsupported engine count\n");
 
diff --git a/lib/i915/gem_engine_topology.h b/lib/i915/gem_engine_topology.h
index 2415fd1e3..a1018afca 100644
--- a/lib/i915/gem_engine_topology.h
+++ b/lib/i915/gem_engine_topology.h
@@ -30,9 +30,7 @@
 #define GEM_MAX_ENGINES		I915_EXEC_RING_MASK + 1
 
 struct intel_engine_data {
-	uint32_t nengines;
-	uint32_t n;
-	struct intel_execution_engine2 *current_engine;
+	uint32_t nengines, cur;
 	struct intel_execution_engine2 engines[GEM_MAX_ENGINES];
 };
 
@@ -40,31 +38,43 @@ bool gem_has_engine_topology(int fd);
 struct intel_engine_data intel_init_engine_list(int fd, uint32_t ctx_id);
 
 /* iteration functions */
-struct intel_execution_engine2 *
-intel_get_current_engine(struct intel_engine_data *ed);
-
-struct intel_execution_engine2 *
-intel_get_current_physical_engine(struct intel_engine_data *ed);
-
-void intel_next_engine(struct intel_engine_data *ed);
-
 int gem_context_lookup_engine(int fd, uint64_t engine, uint32_t ctx_id,
 			      struct intel_execution_engine2 *e);
 
 void gem_context_set_all_engines(int fd, uint32_t ctx);
 
+static inline struct intel_execution_engine2 *
+intel_get_current_engine(struct intel_engine_data *ed)
+{
+	if (ed->cur >= ed->nengines)
+		return NULL;
+
+	return &ed->engines[ed->cur];
+}
+
+static inline struct intel_execution_engine2 *
+intel_get_current_physical_engine(struct intel_engine_data *ed)
+{
+	struct intel_execution_engine2 *e;
+
+	for (; (e = intel_get_current_engine(ed)) && e->is_virtual; ed->cur++)
+		;
+
+	return e;
+}
+
 #define __for_each_static_engine(e__) \
 	for ((e__) = intel_execution_engines2; (e__)->name; (e__)++)
 
 #define for_each_context_engine(fd__, ctx__, e__) \
 	for (struct intel_engine_data i__ = intel_init_engine_list(fd__, ctx__); \
 	     ((e__) = intel_get_current_engine(&i__)); \
-	     intel_next_engine(&i__))
+	     i__.cur++)
 
 /* needs to replace "for_each_physical_engine" when conflicts are fixed */
 #define __for_each_physical_engine(fd__, e__) \
 	for (struct intel_engine_data i__ = intel_init_engine_list(fd__, 0); \
 	     ((e__) = intel_get_current_physical_engine(&i__)); \
-	     intel_next_engine(&i__))
+	     i__.cur++)
 
 #endif /* GEM_ENGINE_TOPOLOGY_H */
-- 
2.20.1