From 2d864e41710f1d2ba406fb62018ab0487152e6f2 Mon Sep 17 00:00:00 2001 From: Anatol Pomozov Date: Tue, 7 May 2013 15:37:48 -0700 Subject: [PATCH] kref: minor cleanup - make warning smp-safe - result of atomic _unless_zero functions should be checked by caller to avoid use-after-free error - trivial whitespace fix. Link: https://lkml.org/lkml/2013/4/12/391 Tested: compile x86, boot machine and run xfstests Signed-off-by: Anatol Pomozov [ Removed line-break, changed to use WARN_ON_ONCE() - Linus ] Signed-off-by: Linus Torvalds --- include/linux/kref.h | 9 ++++++--- lib/kobject.c | 2 +- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/include/linux/kref.h b/include/linux/kref.h index 4972e6e9ca93..e15828fd71f1 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -39,8 +39,11 @@ static inline void kref_init(struct kref *kref) */ static inline void kref_get(struct kref *kref) { - WARN_ON(!atomic_read(&kref->refcount)); - atomic_inc(&kref->refcount); + /* If refcount was 0 before incrementing then we have a race + * condition when this kref is freeing by some other thread right now. + * In this case one should use kref_get_unless_zero() + */ + WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2); } /** @@ -100,7 +103,7 @@ static inline int kref_put_mutex(struct kref *kref, struct mutex *lock) { WARN_ON(release == NULL); - if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) { + if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) { mutex_lock(lock); if (unlikely(!atomic_dec_and_test(&kref->refcount))) { mutex_unlock(lock); diff --git a/lib/kobject.c b/lib/kobject.c index a65486613d79..b7e29a6056d3 100644 --- a/lib/kobject.c +++ b/lib/kobject.c @@ -529,7 +529,7 @@ struct kobject *kobject_get(struct kobject *kobj) return kobj; } -static struct kobject *kobject_get_unless_zero(struct kobject *kobj) +static struct kobject * __must_check kobject_get_unless_zero(struct kobject *kobj) { if (!kref_get_unless_zero(&kobj->kref)) kobj = NULL; -- 2.30.2