From 2d864e41710f1d2ba406fb62018ab0487152e6f2 Mon Sep 17 00:00:00 2001
From: Anatol Pomozov <anatol.pomozov@gmail.com>
Date: Tue, 7 May 2013 15:37:48 -0700
Subject: 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 <anatol.pomozov@gmail.com>
[ Removed line-break, changed to use WARN_ON_ONCE()  - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/kref.h b/include/linux/kref.h
index 4972e6e..e15828f 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 a654866..b7e29a6 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;
-- 
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