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

[Tvrtko Ursulin]

On 29/05/2019 14:24, Chris Wilson wrote:
> 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.

We had one infinite loop in there already.. AFAIR it was on one engine 
platforms. Does the new incarnation happen actually via the 
__for_each_physical_engine iterator or perhaps only when calling 
intel_get_current_physical_engine after loop end? Why it wasn't seen in 
testing?

Regards,

Tvrtko

> 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 */
>