[PATCH 43/79] drm/i915: Use fault-injection to force the shrinker to run in live GTT tests

[Chris Wilson]

It is possible whilst allocating the page-directory tree for a ppgtt
bind that the shrinker may run and reap unused parts of the tree. If the
shrinker happens to remove a chunk of the tree that the
allocate_va_range has already processed, we may then try to insert into
the dangling tree. This test uses the fault-injection framework to force
the shrinker to be invoked before we allocate new pages, i.e. new chunks
of the PD tree.

References: https://bugs.freedesktop.org/show_bug.cgi?id=99295
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/Kconfig.debug            |  1 +
 drivers/gpu/drm/i915/i915_drv.h               |  2 ++
 drivers/gpu/drm/i915/i915_gem_gtt.c           |  6 ++++++
 drivers/gpu/drm/i915/i915_selftest.h          |  2 ++
 drivers/gpu/drm/i915/selftests/i915_gem_gtt.c | 29 +++++++++++++++++++++++++++
 5 files changed, 40 insertions(+)

diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
index a4d8cfd77c3c..68ff072f8b76 100644
--- a/drivers/gpu/drm/i915/Kconfig.debug
+++ b/drivers/gpu/drm/i915/Kconfig.debug
@@ -65,6 +65,7 @@ config DRM_I915_SELFTEST
 	bool "Enable selftests upon driver load"
 	depends on DRM_I915
 	default n
+	select FAULT_INJECTION
 	select PRIME_NUMBERS
 	help
 	  Choose this option to allow the driver to perform selftests upon
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 56a3de94ecf4..f298da9eaebc 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2468,6 +2468,8 @@ struct drm_i915_private {
 		int	irq;
 	} lpe_audio;
 
+	I915_SELFTEST_DECLARE(struct fault_attr vm_fault);
+
 	/*
 	 * NOTE: This is the dri1/ums dungeon, don't add stuff here. Your patch
 	 * will be rejected. Instead look for a better place.
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 36142d3d99d2..0247b26265dd 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -23,6 +23,9 @@
  *
  */
 
+#include <linux/slab.h> /* fault-inject.h is not standalone! */
+
+#include <linux/fault-inject.h>
 #include <linux/log2.h>
 #include <linux/random.h>
 #include <linux/seq_file.h>
@@ -345,6 +348,9 @@ static int __setup_page_dma(struct drm_i915_private *dev_priv,
 {
 	struct device *kdev = &dev_priv->drm.pdev->dev;
 
+	if (I915_SELFTEST_ONLY(should_fail(&dev_priv->vm_fault, 1)))
+		i915_gem_shrink_all(dev_priv);
+
 	p->page = alloc_page(flags);
 	if (!p->page)
 		return -ENOMEM;
diff --git a/drivers/gpu/drm/i915/i915_selftest.h b/drivers/gpu/drm/i915/i915_selftest.h
index e43777b72211..9d7d86f1733d 100644
--- a/drivers/gpu/drm/i915/i915_selftest.h
+++ b/drivers/gpu/drm/i915/i915_selftest.h
@@ -36,6 +36,8 @@ struct i915_selftest {
 };
 
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
+#include <linux/fault-inject.h>
+
 extern struct i915_selftest i915_selftest;
 
 int i915_mock_selftests(void);
diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c b/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
index 98b3bc1af62a..39a42a19fa9f 100644
--- a/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
@@ -675,6 +675,29 @@ static int drunk_hole(struct drm_i915_private *i915,
 	return 0;
 }
 
+static int shrink_hole(struct drm_i915_private *i915,
+		       struct i915_address_space *vm,
+		       u64 hole_start, u64 hole_end,
+		       unsigned long end_time)
+{
+	unsigned long prime;
+	int err;
+
+	i915->vm_fault.probability = 999;
+	atomic_set(&i915->vm_fault.times, -1);
+
+	for_each_prime_number_from(prime, 0, ULONG_MAX - 1) {
+		i915->vm_fault.interval = prime;
+		err = drunk_hole(i915, vm, hole_start, hole_end, end_time);
+		if (err)
+			break;
+	}
+
+	memset(&i915->vm_fault, 0, sizeof(i915->vm_fault));
+
+	return err;
+}
+
 static int exercise_ppgtt(struct drm_i915_private *dev_priv,
 			  int (*func)(struct drm_i915_private *i915,
 				      struct i915_address_space *vm,
@@ -732,6 +755,11 @@ static int igt_ppgtt_lowlevel(void *arg)
 	return exercise_ppgtt(arg, lowlevel_hole);
 }
 
+static int igt_ppgtt_shrink(void *arg)
+{
+	return exercise_ppgtt(arg, shrink_hole);
+}
+
 static int sort_holes(void *priv, struct list_head *A, struct list_head *B)
 {
 	struct drm_mm_node *a = list_entry(A, typeof(*a), hole_stack);
@@ -809,6 +837,7 @@ int i915_gem_gtt_live_selftests(struct drm_i915_private *i915)
 		SUBTEST(igt_ppgtt_drunk),
 		SUBTEST(igt_ppgtt_walk),
 		SUBTEST(igt_ppgtt_fill),
+		SUBTEST(igt_ppgtt_shrink),
 		SUBTEST(igt_ggtt_lowlevel),
 		SUBTEST(igt_ggtt_drunk),
 		SUBTEST(igt_ggtt_walk),
-- 
2.11.0