[PATCH v2] kref: warn on uninitialized kref

[Mikulas Patocka]

I found a memory leak in iSCSI target that was caused by kref initialized
to zero (the memory object was allocated with kzalloc, kref_init was not
called and kref_put_spinlock_irqsave was called which changed "0" to "-1"
and didn't free the object).

Similar bugs may exist in other kernel areas, so I submit this patch that
adds a check to kref.h. If the value is zero or negative, we can assume
that it is uninitialized and we warn about it.

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>

---
 include/linux/kref.h |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-3.15-rc5/include/linux/kref.h
===================================================================
--- linux-3.15-rc5.orig/include/linux/kref.h	2014-05-16 19:00:18.000000000 +0200
+++ linux-3.15-rc5/include/linux/kref.h	2014-05-17 13:19:31.000000000 +0200
@@ -69,7 +69,7 @@ static inline int kref_sub(struct kref *
 	     void (*release)(struct kref *kref))
 {
 	WARN_ON(release == NULL);
-
+	WARN_ON_ONCE(atomic_read(&kref->refcount) < (int)count);
 	if (atomic_sub_and_test((int) count, &kref->refcount)) {
 		release(kref);
 		return 1;
@@ -119,6 +119,7 @@ static inline int kref_put_spinlock_irqs
 	unsigned long flags;
 
 	WARN_ON(release == NULL);
+	WARN_ON_ONCE(atomic_read(&kref->refcount) <= 0);
 	if (atomic_add_unless(&kref->refcount, -1, 1))
 		return 0;
 	spin_lock_irqsave(lock, flags);
@@ -136,6 +137,7 @@ static inline int kref_put_mutex(struct 
 				 struct mutex *lock)
 {
 	WARN_ON(release == NULL);
+	WARN_ON_ONCE(atomic_read(&kref->refcount) <= 0);
 	if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) {
 		mutex_lock(lock);
 		if (unlikely(!atomic_dec_and_test(&kref->refcount))) {

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