linux-kernel - [PATCH 3/4] kmemleak: Store object reverse references for debugging purposes

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Date:	Mon, 19 Oct 2009 15:49:34 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] kmemleak: Store object reverse references for debugging
	purposes

There are some memory leak reports which come and go but are hard to
identify whether they are false positives or not. This patch stores up
to 4 reverse references in an object so that once a leak disappeared,
using "echo dump=<ptr> > debug/kmemleak" would list where an object is
referenced from.

Signed-off-by: Catalin Marinas <catalin.marinas@....com>
---
 mm/kmemleak.c |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 9610635..998162f 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -110,6 +110,7 @@
 #define SECS_SCAN_WAIT		600	/* subsequent auto scanning delay */
 #define GRAY_LIST_PASSES	25	/* maximum number of gray list scans */
 #define MAX_SCAN_SIZE		4096	/* maximum size of a scanned block */
+#define MAX_REV_REF		4	/* number of reverse references */
 
 #define BYTES_PER_POINTER	sizeof(void *)
 
@@ -156,6 +157,7 @@ struct kmemleak_object {
 	unsigned long jiffies;		/* creation timestamp */
 	pid_t pid;			/* pid of the current task */
 	char comm[TASK_COMM_LEN];	/* executable name */
+	void *rev_ref[MAX_REV_REF];	/* reverse references */
 };
 
 /* flag representing the memory block allocation status */
@@ -379,6 +381,13 @@ static void dump_object_info(struct kmemleak_object *object)
 	pr_notice("  min_count = %d\n", object->min_count);
 	pr_notice("  count = %d\n", object->count);
 	pr_notice("  flags = 0x%lx\n", object->flags);
+	if (object->count) {
+		int i;
+		pr_notice("  referred from:");
+		for (i = 0; i < object->count; i++)
+			printk(" 0x%p", object->rev_ref[i]);
+		printk("\n");
+	}
 	pr_notice("  backtrace:\n");
 	print_stack_trace(&trace, 4);
 }
@@ -1011,8 +1020,12 @@ static void scan_block(void *_start, void *_end,
 		 */
 		spin_lock_irqsave_nested(&object->lock, flags,
 					 SINGLE_DEPTH_NESTING);
+		if (object->count < MAX_REV_REF)
+			object->rev_ref[object->count] = ptr;
+
 		if (!color_white(object)) {
 			/* non-orphan, ignored or new */
+			object->count++;
 			spin_unlock_irqrestore(&object->lock, flags);
 			put_object(object);
 			continue;
@@ -1416,7 +1429,7 @@ static int dump_str_object_info(const char *str)
 	unsigned long addr;
 
 	addr= simple_strtoul(str, NULL, 0);
-	object = find_and_get_object(addr, 0);
+	object = find_and_get_object(addr, 1);
 	if (!object) {
 		pr_info("Unknown object at 0x%08lx\n", addr);
 		return -EINVAL;

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