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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

From: Tvrtko Ursulin <tvrtko.ursulin@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@intel.com>
Cc: Chris Wilson <chris@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);
+			*unlock = true;
 		}
 		return *unlock;
 
-- 
2.19.1

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