1 files changed, 39 insertions, 3 deletions

diff --git a/include/linux/kref.h b/include/linux/kref.h
index 4972e6e9ca93..484604d184be 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -19,6 +19,7 @@
 #include <linux/atomic.h>
 #include <linux/kernel.h>
 #include <linux/mutex.h>
+#include <linux/spinlock.h>
 
 struct kref {
         atomic_t refcount;
@@ -39,8 +40,11 @@ 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);
 }
 
 /**
@@ -95,12 +99,44 @@ static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)
         return kref_sub(kref, 1, release);
 }
 
+/**
+ * kref_put_spinlock_irqsave - decrement refcount for object.
+ * @kref: object.
+ * @release: pointer to the function that will clean up the object when the
+ *           last reference to the object is released.
+ *           This pointer is required, and it is not acceptable to pass kfree
+ *           in as this function.
+ * @lock: lock to take in release case
+ *
+ * Behaves identical to kref_put with one exception.  If the reference count
+ * drops to zero, the lock will be taken atomically wrt dropping the reference
+ * count.  The release function has to call spin_unlock() without _irqrestore.
+ */
+static inline int kref_put_spinlock_irqsave(struct kref *kref,
+                void (*release)(struct kref *kref),
+                spinlock_t *lock)
+{
+        unsigned long flags;
+
+        WARN_ON(release == NULL);
+        if (atomic_add_unless(&kref->refcount, -1, 1))
+                return 0;
+        spin_lock_irqsave(lock, flags);
+        if (atomic_dec_and_test(&kref->refcount)) {
+                release(kref);
+                local_irq_restore(flags);
+                return 1;
+        }
+        spin_unlock_irqrestore(lock, flags);
+        return 0;
+}
+
 static inline int kref_put_mutex(struct kref *kref,
                                  void (*release)(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);