Messages in this thread Patch in this message |  | | From | Catalin Marinas <> | Subject | [PATCH v2 2/4] mm: kmemleak: Fix delete_object_*() race when called on the same memory block | Date | Mon, 8 Jun 2015 15:29:16 +0100 |
| |
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> Cc: Andrew Morton <akpm@linux-foundation.org> --- mm/kmemleak.c | 39 ++++++++++++++++++++++++++------------- 1 file changed, 26 insertions(+), 13 deletions(-)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 41df5b8efd25..ecde522ff616 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -498,6 +498,27 @@ static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias) } /* + * 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 @@ 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)
|  |