Commit e781a9ab authored by Catalin Marinas's avatar Catalin Marinas Committed by Linus Torvalds
Browse files

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: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c5f3b1a5

mm/kmemleak.c

+26 −13
Original line number Diff line number Diff line
@@ -497,6 +497,27 @@ static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias) 
	return object;

}



/*

 * 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.

 */
@@ -600,20 +621,14 @@ out: 
}



/*

 * 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 @@ static void delete_object_full(unsigned long ptr) 
{

	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 @@ static void delete_object_full(unsigned long ptr) 
		return;

	}

	__delete_object(object);

	put_object(object);

}



/*
@@ -655,7 +669,7 @@ static void delete_object_part(unsigned long ptr, size_t size) 
	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 @@ static void delete_object_part(unsigned long ptr, size_t size) 
#endif

		return;

	}

	__delete_object(object);



	/*

	 * Create one or two objects that may result from the memory block
@@ -681,7 +694,7 @@ static void delete_object_part(unsigned long ptr, size_t size) 
		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)

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