[Intel-gfx] [RFC 4/4] drm/i915: Remove trylock-looping from the shrinker

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-01-03 12:23:29)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> In a patch named "drm/i915: Return immediately if trylock fails for
> direct-reclaim" Chris Wilson implicitly suggests it is safe to use a plain
> mutex_lock instead of trylock on the I915_SHRINK_ACTIVE code paths.
> 
> Explore this to see how the lockdep traces will look.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem_shrinker.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> index 97deec775f40..2d4a54851c0a 100644
> --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
> +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> @@ -47,15 +47,8 @@ shrinker_lock(struct drm_i915_private *i915, unsigned int flags, bool *unlock)
>         case MUTEX_TRYLOCK_FAILED:
>                 *unlock = false;
>                 if (flags & I915_SHRINK_ACTIVE) {
> -                       preempt_disable();
> -                       do {
> -                               cpu_relax();
> -                               if (mutex_trylock(&i915->drm.struct_mutex)) {
> -                                       *unlock = true;
> -                                       break;
> -                               }
> -                       } while (!need_resched());
> -                       preempt_enable();
> +                       mutex_lock(&i915->drm.struct_mutex);

You seemed to have lost some annotation here.
-Chris