[Intel-gfx] [PATCH] drm/i915: Fix waiting for engines to idle

[Tvrtko Ursulin]

On 23/05/2017 12:30, Jani Nikula wrote:
> On Tue, 23 May 2017, Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com> wrote:
>> On 23/05/2017 10:56, Jani Nikula wrote:
>>> On Tue, 23 May 2017, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>>>> On Tue, May 23, 2017 at 10:19:31AM +0100, Tvrtko Ursulin wrote:
>>>>> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>>>>
>>>>> Waiting for engines needs to happen even in the non-debug builds
>>>>> so it is incorrect to wrap it in a GEM_WARN_ON.
>>>>>
>>>>> Call it unconditionally and add GEM_WARN so that the debug
>>>>> warning can still be emitted when things go bad.
>>>>>
>>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>>>> Fixes: 25112b64b3d2 ("drm/i915: Wait for all engines to be idle as part of i915_gem_wait_for_idle()")
>>>>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>>>>> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
>>>>> Cc: Daniel Vetter <daniel.vetter at intel.com>
>>>>> Cc: Jani Nikula <jani.nikula at linux.intel.com>
>>>>> Cc: intel-gfx at lists.freedesktop.org
>>>>> Reported-by: Nick Desaulniers <nick.desaulniers at gmail.com>
>>>>> Cc: Nick Desaulniers <nick.desaulniers at gmail.com>
>>>>> ---
>>>>>  drivers/gpu/drm/i915/i915_gem.c | 3 ++-
>>>>>  drivers/gpu/drm/i915/i915_gem.h | 2 ++
>>>>>  2 files changed, 4 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>>>>> index a637cc05cc4a..ecaa21f106c8 100644
>>>>> --- a/drivers/gpu/drm/i915/i915_gem.c
>>>>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>>>>> @@ -3332,7 +3332,8 @@ static int wait_for_engines(struct drm_i915_private *i915)
>>>>>  	enum intel_engine_id id;
>>>>>
>>>>>  	for_each_engine(engine, i915, id) {
>>>>> -		if (GEM_WARN_ON(wait_for_engine(engine, 50))) {
>>>>> +		if (wait_for_engine(engine, 50)) {
>>>>> +			GEM_WARN(1, "%s wait for idle timeout", engine->name);
>>>>
>>>> Nice touching adding the engine->name
>>>> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
>>>>
>>>>>  			i915_gem_set_wedged(i915);
>>>>>  			return -EIO;
>>>>>  		}
>>>>> diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
>>>>> index ee54597465b6..cefc6cf96a60 100644
>>>>> --- a/drivers/gpu/drm/i915/i915_gem.h
>>>>> +++ b/drivers/gpu/drm/i915/i915_gem.h
>>>>> @@ -30,6 +30,7 @@
>>>>>  #ifdef CONFIG_DRM_I915_DEBUG_GEM
>>>>>  #define GEM_BUG_ON(expr) BUG_ON(expr)
>>>>>  #define GEM_WARN_ON(expr) WARN_ON(expr)
>>>>> +#define GEM_WARN(condition, format, ...) WARN(condition, format, __VA_ARGS__)
>>>>>
>>>>>  #define GEM_DEBUG_DECL(var) var
>>>>>  #define GEM_DEBUG_EXEC(expr) expr
>>>>> @@ -38,6 +39,7 @@
>>>>>  #else
>>>>>  #define GEM_BUG_ON(expr) BUILD_BUG_ON_INVALID(expr)
>>>>>  #define GEM_WARN_ON(expr) (BUILD_BUG_ON_INVALID(expr), 0)
>>>>> +#define GEM_WARN(condition, format, ...) BUILD_BUG_ON_INVALID(condition)
>>>>
>>>> WARNs can be used as part of an if(), so perhaps
>>>>
>>>> #define GEM_WARN(condition, format, ...) (BUILD_BUG_ON_INVALID(condition), 0)
>>>> #define GEM_WARN_ON(expr) GEM_WARN((expr), 0)
>>>
>>> Sorry, I just can't resist the "told you so" here.
>>>
>>> If you come up with a local pattern that's deceptively similar to a
>>> widely used one, with the crucial difference that you can't use anything
>>> with required side effects in it, you'll screw it up eventually.
>>>
>>> if (GEM_WARN_ON(wait_for_engine(engine, 50))) looks completely natural
>>> and "obviously correct" in code, but is dead wrong. This won't be the
>>> last time.
>>
>> I would also prefer to make it consistent.
>>
>> There are two other users of GEM_WARN_ON in i915_vma_bind to consider
>> what to do with, but anyway it would be a much better solution.
>
> My suggestion is to make GEM_WARN_ON and friends that are conditional to
> CONFIG_DRM_I915_DEBUG_GEM unusable as expressions. Make them fail to
> build within if (...) for both CONFIG_DRM_I915_DEBUG_GEM=y and =n. Then
> if you need that kind of construct, handle it with something like:
>
> 	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && condition) {
> 		GEM_WARN(...);
> 		...
> 	}
>
> maybe wrapping that IS_ENABLED bit in a more manageable macro.

Why not simply make it work like a normal WARN_ON? Eg:

#ifdef ...DEBUG_GEM
#define GEM_WARN_ON(expr) WARN_ON(expr)
#else
#define GEM_WARN_ON(expr) (expr)
#endif

Regards,

Tvrtko