From 9d5a4c730dd164f6f1b4ed6690fbe2667e5149ea Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Wed, 24 Jun 2015 16:58:34 -0700 Subject: mm: kmemleak: avoid deadlock on the kmemleak object insertion error path While very unlikely (usually kmemleak or sl*b bug), the create_object() function in mm/kmemleak.c may fail to insert a newly allocated object into the rb tree. When this happens, kmemleak disables itself and prints additional information about the object already found in the rb tree. Such printing is done with the parent->lock acquired, however the kmemleak_lock is already held. This is a potential race with the scanning thread which acquires object->lock and kmemleak_lock in a This patch removes the locking around the 'parent' object information printing. Such object cannot be freed or removed from object_tree_root and object_list since kmemleak_lock is already held. There is a very small risk that some of the object data is being modified on another CPU but the only downside is inconsistent information printing. Signed-off-by: Catalin Marinas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 8a57e34..c0fd776 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -53,6 +53,11 @@ * modifications to the memory scanning parameters including the scan_thread * pointer * + * Locks and mutexes should only be acquired/nested in the following order: + * + * scan_mutex -> object->lock -> other_object->lock (SINGLE_DEPTH_NESTING) + * -> kmemleak_lock + * * The kmemleak_object structures have a use_count incremented or decremented * using the get_object()/put_object() functions. When the use_count becomes * 0, this count can no longer be incremented and put_object() schedules the @@ -603,11 +608,13 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size, kmemleak_stop("Cannot insert 0x%lx into the object " "search tree (overlaps existing)\n", ptr); + /* + * No need for parent->lock here since "parent" cannot + * be freed while the kmemleak_lock is held. + */ + dump_object_info(parent); kmem_cache_free(object_cache, object); - object = parent; - spin_lock(&object->lock); - dump_object_info(object); - spin_unlock(&object->lock); + object = NULL; goto out; } } -- cgit v0.10.2