mm: kmemleak: fix delete_object_*() race when called on the same memory block
Calling delete_object_*() on the same pointer is not a standard use case
(unless there is a bug in the code calling kmemleak_free()). However,
during kmemleak disabling (error or user triggered via /sys), there is a
potential race between kmemleak_free() calls on a CPU and
__kmemleak_do_cleanup() on a different CPU.
The current delete_object_*() implementation first performs a look-up
holding kmemleak_lock, increments the object->use_count and then
re-acquires kmemleak_lock to remove the object from object_tree_root and
object_list.
This patch simplifies the delete_object_*() mechanism to both look up
and remove an object from the object_tree_root and object_list
atomically (guarded by kmemleak_lock). This allows safe concurrent
calls to delete_object_*() on the same pointer without additional
locking for synchronising the kmemleak_free_enabled flag.
A side effect is a slight improvement in the delete_object_*() performance
by avoiding acquiring kmemleak_lock twice and incrementing/decrementing
object->use_count.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 41df5b8..ecde522 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -498,6 +498,27 @@
}
/*
+ * Look up an object in the object search tree and remove it from both
+ * object_tree_root and object_list. The returned object's use_count should be
+ * at least 1, as initially set by create_object().
+ */
+static struct kmemleak_object *find_and_remove_object(unsigned long ptr, int alias)
+{
+ unsigned long flags;
+ struct kmemleak_object *object;
+
+ write_lock_irqsave(&kmemleak_lock, flags);
+ object = lookup_object(ptr, alias);
+ if (object) {
+ rb_erase(&object->rb_node, &object_tree_root);
+ list_del_rcu(&object->object_list);
+ }
+ write_unlock_irqrestore(&kmemleak_lock, flags);
+
+ return object;
+}
+
+/*
* Save stack trace to the given array of MAX_TRACE size.
*/
static int __save_stack_trace(unsigned long *trace)
@@ -600,20 +621,14 @@
}
/*
- * Remove the metadata (struct kmemleak_object) for a memory block from the
- * object_list and object_tree_root and decrement its use_count.
+ * Mark the object as not allocated and schedule RCU freeing via put_object().
*/
static void __delete_object(struct kmemleak_object *object)
{
unsigned long flags;
- write_lock_irqsave(&kmemleak_lock, flags);
- rb_erase(&object->rb_node, &object_tree_root);
- list_del_rcu(&object->object_list);
- write_unlock_irqrestore(&kmemleak_lock, flags);
-
WARN_ON(!(object->flags & OBJECT_ALLOCATED));
- WARN_ON(atomic_read(&object->use_count) < 2);
+ WARN_ON(atomic_read(&object->use_count) < 1);
/*
* Locking here also ensures that the corresponding memory block
@@ -633,7 +648,7 @@
{
struct kmemleak_object *object;
- object = find_and_get_object(ptr, 0);
+ object = find_and_remove_object(ptr, 0);
if (!object) {
#ifdef DEBUG
kmemleak_warn("Freeing unknown object at 0x%08lx\n",
@@ -642,7 +657,6 @@
return;
}
__delete_object(object);
- put_object(object);
}
/*
@@ -655,7 +669,7 @@
struct kmemleak_object *object;
unsigned long start, end;
- object = find_and_get_object(ptr, 1);
+ object = find_and_remove_object(ptr, 1);
if (!object) {
#ifdef DEBUG
kmemleak_warn("Partially freeing unknown object at 0x%08lx "
@@ -663,7 +677,6 @@
#endif
return;
}
- __delete_object(object);
/*
* Create one or two objects that may result from the memory block
@@ -681,7 +694,7 @@
create_object(ptr + size, end - ptr - size, object->min_count,
GFP_KERNEL);
- put_object(object);
+ __delete_object(object);
}
static void __paint_it(struct kmemleak_object *object, int color)