[PATCH 1/2] drm: Track drm_mm allocators and show leaks on shutdown

[Chris Wilson]

We can use the kernel's stack tracer and depot to record the allocation
site of every drm_mm user and then on shutdown as well as warning that
allocated nodes still reside with the drm_mm range manager, we can also
display who allocated them to aide tracking down the leak.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/Kconfig  | 12 ++++++++
 drivers/gpu/drm/drm_mm.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++--
 include/drm/drm_mm.h     |  6 ++++
 3 files changed, 89 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 483059a22b1b..e339ac9ca8cf 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -300,3 +300,15 @@ config DRM_SAVAGE
 	  chipset. If M is selected the module will be called savage.
 
 endif # DRM_LEGACY
+
+config DRM_DEBUG_MM
+	bool "Insert extra checks for tracking the memory manager"
+	default n
+	depends on DRM
+	select STACKDEPOT
+	help
+	  Enable tracking of memory manager and leak detection.
+
+	  Recommended for driver developers only.
+
+	  If in doubt, say "N".
diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 11d44a1e0ab3..f7d25c02297d 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -104,6 +104,66 @@ static struct drm_mm_node *drm_mm_search_free_in_range_generic(const struct drm_
 						u64 end,
 						enum drm_mm_search_flags flags);
 
+#if CONFIG_DRM_DEBUG_MM
+#define STACKDEPTH 32
+#define BUFSZ 4096
+
+static noinline void save_stack(struct drm_mm_node *node)
+{
+	unsigned long entries[STACKDEPTH];
+	struct stack_trace trace = {
+		.entries = entries,
+		.max_entries = STACKDEPTH,
+		.skip = 1
+	};
+
+	save_stack_trace(&trace);
+	if (trace.nr_entries != 0 &&
+	    trace.entries[trace.nr_entries-1] == ULONG_MAX)
+		trace.nr_entries--;
+
+	/* May be called under spinlock, so avoid sleeping */
+	node->stack = depot_save_stack(&trace, GFP_NOWAIT);
+}
+
+static void show_leaks(struct drm_mm *mm)
+{
+	struct drm_mm_node *node;
+	unsigned long entries[STACKDEPTH];
+	char *buf;
+
+	buf = kmalloc(BUFSZ, GFP_KERNEL);
+	if (!buf)
+		return;
+
+	list_for_each_entry(node, &mm->head_node.node_list, node_list) {
+		struct stack_trace trace = {
+			.entries = entries,
+			.max_entries = STACKDEPTH
+		};
+
+		if (!node->stack) {
+			DRM_ERROR("node [%08llx + %08llx]: unknown owner\n",
+				  node->start, node->size);
+			continue;
+		}
+
+		depot_fetch_stack(node->stack, &trace);
+		snprint_stack_trace(buf, BUFSZ, &trace, 0);
+		DRM_ERROR("node [%08llx + %08llx]: inserted at\n%s",
+			  node->start, node->size, buf);
+	}
+
+	kfree(buf);
+}
+
+#undef STACKDEPTH
+#undef BUFSZ
+#else
+static void save_stack(struct drm_mm_node *node) { }
+static void show_leaks(struct drm_mm *mm) { }
+#endif
+
 #define START(node) ((node)->start)
 #define LAST(node)  ((node)->start + (node)->size - 1)
 
@@ -228,6 +288,8 @@ static void drm_mm_insert_helper(struct drm_mm_node *hole_node,
 		list_add(&node->hole_stack, &mm->hole_stack);
 		node->hole_follows = 1;
 	}
+
+	save_stack(node);
 }
 
 /**
@@ -293,6 +355,8 @@ int drm_mm_reserve_node(struct drm_mm *mm, struct drm_mm_node *node)
 		node->hole_follows = 1;
 	}
 
+	save_stack(node);
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_mm_reserve_node);
@@ -397,6 +461,8 @@ static void drm_mm_insert_helper_range(struct drm_mm_node *hole_node,
 		list_add(&node->hole_stack, &mm->hole_stack);
 		node->hole_follows = 1;
 	}
+
+	save_stack(node);
 }
 
 /**
@@ -861,10 +927,12 @@ EXPORT_SYMBOL(drm_mm_init);
  * Note that it is a bug to call this function on an allocator which is not
  * clean.
  */
-void drm_mm_takedown(struct drm_mm * mm)
+void drm_mm_takedown(struct drm_mm *mm)
 {
-	WARN(!list_empty(&mm->head_node.node_list),
-	     "Memory manager not clean during takedown.\n");
+	if (WARN(!list_empty(&mm->head_node.node_list),
+		 "Memory manager not clean during takedown.\n"))
+		show_leaks(mm);
+
 }
 EXPORT_SYMBOL(drm_mm_takedown);
 
diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
index 205ddcf6d55d..41ddafe92b2f 100644
--- a/include/drm/drm_mm.h
+++ b/include/drm/drm_mm.h
@@ -44,6 +44,9 @@
 #ifdef CONFIG_DEBUG_FS
 #include <linux/seq_file.h>
 #endif
+#ifdef CONFIG_DRM_DEBUG_MM
+#include <linux/stackdepot.h>
+#endif
 
 enum drm_mm_search_flags {
 	DRM_MM_SEARCH_DEFAULT =		0,
@@ -74,6 +77,9 @@ struct drm_mm_node {
 	u64 size;
 	u64 __subtree_last;
 	struct drm_mm *mm;
+#ifdef CONFIG_DRM_DEBUG_MM
+	depot_stack_handle_t stack;
+#endif
 };
 
 struct drm_mm {
-- 
2.10.1