From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Tue, 3 Jul 2018 11:18:29 +0100
Subject: drm/i915/selftests: Release the struct_mutex to free the objects
Git-commit: 38b7fb0b2ad1f2ba83bf9a8535cedb198a448ea4
Patch-mainline: v4.19-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

live_gtt is a very slow test to run, simply because it tries to allocate
and use as much as the 48b address space as possibly can and in the
process will try to own all of the system memory. This leads to resource
exhaustion and CPU starvation; the latter impacts us when the NMI
watchdog declares a task hung due to a mutex contention with ourselves.
This we can prevent by releasing the struct_mutex and forcing our
i915/rcu workers to run, and in particular flushing the freed object
worker that is the cause for concern.

References: https://bugs.freedesktop.org/show_bug.cgi?id=107094
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703101829.7360-1-chris@chris-wilson.co.uk

Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/i915/selftests/i915_gem_gtt.c |   23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

--- a/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
@@ -32,6 +32,20 @@
 #include "mock_drm.h"
 #include "mock_gem_device.h"
 
+static void cleanup_freed_objects(struct drm_i915_private *i915)
+{
+	/*
+	 * As we may hold onto the struct_mutex for inordinate lengths of
+	 * time, the NMI khungtaskd detector may fire for the free objects
+	 * worker.
+	 */
+	mutex_unlock(&i915->drm.struct_mutex);
+
+	i915_gem_drain_freed_objects(i915);
+
+	mutex_lock(&i915->drm.struct_mutex);
+}
+
 static void fake_free_pages(struct drm_i915_gem_object *obj,
 			    struct sg_table *pages)
 {
@@ -291,6 +305,8 @@ static int lowlevel_hole(struct drm_i915
 		i915_gem_object_put(obj);
 
 		kfree(order);
+
+		cleanup_freed_objects(i915);
 	}
 
 	return 0;
@@ -519,6 +535,7 @@ static int fill_hole(struct drm_i915_pri
 		}
 
 		close_object_list(&objects, vm);
+		cleanup_freed_objects(i915);
 	}
 
 	return 0;
@@ -605,6 +622,8 @@ err_put:
 		i915_gem_object_put(obj);
 		if (err)
 			return err;
+
+		cleanup_freed_objects(i915);
 	}
 
 	return 0;
@@ -789,6 +808,8 @@ err_obj:
 		kfree(order);
 		if (err)
 			return err;
+
+		cleanup_freed_objects(i915);
 	}
 
 	return 0;
@@ -857,6 +878,7 @@ static int __shrink_hole(struct drm_i915
 	}
 
 	close_object_list(&objects, vm);
+	cleanup_freed_objects(i915);
 	return err;
 }
 
@@ -949,6 +971,7 @@ static int shrink_boom(struct drm_i915_p
 		i915_gem_object_put(explode);
 
 		memset(&vm->fault_attr, 0, sizeof(vm->fault_attr));
+		cleanup_freed_objects(i915);
 	}
 
 	return 0;