drm/i915/gem: Break up long lists of object reclaim

Call cond_resched() between each freed object in case we have a really,
really long list, and we don't want to block normal processes.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200221100953.2587176-1-chris@chris-wilson.co.uk
(cherry picked from commit deeee411)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -225,6 +225,7 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
 
 		/* But keep the pointer alive for RCU-protected lookups */
 		call_rcu(&obj->rcu, __i915_gem_free_object_rcu);
+		cond_resched();
 	}
 	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
 }