1 files changed, 49 insertions, 1 deletions

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 6d843d60690d..dd2a08600453 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -63,13 +63,30 @@ struct percpu_ref {
 	 */
 	unsigned __percpu	*pcpu_count;
 	percpu_ref_func_t	*release;
+	percpu_ref_func_t	*confirm_kill;
 	struct rcu_head		rcu;
 };
 
 int __must_check percpu_ref_init(struct percpu_ref *ref,
 				 percpu_ref_func_t *release);
 void percpu_ref_cancel_init(struct percpu_ref *ref);
-void percpu_ref_kill(struct percpu_ref *ref);
+void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
+				 percpu_ref_func_t *confirm_kill);
+
+/**
+ * percpu_ref_kill - drop the initial ref
+ * @ref: percpu_ref to kill
+ *
+ * Must be used to drop the initial ref on a percpu refcount; must be called
+ * precisely once before shutdown.
+ *
+ * Puts @ref in non percpu mode, then does a call_rcu() before gathering up the
+ * percpu counters and dropping the initial ref.
+ */
+static inline void percpu_ref_kill(struct percpu_ref *ref)
+{
+	return percpu_ref_kill_and_confirm(ref, NULL);
+}
 
 #define PCPU_STATUS_BITS	2
 #define PCPU_STATUS_MASK	((1 << PCPU_STATUS_BITS) - 1)
@@ -101,6 +118,37 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
 }
 
 /**
+ * percpu_ref_tryget - try to increment a percpu refcount
+ * @ref: percpu_ref to try-get
+ *
+ * Increment a percpu refcount unless it has already been killed.  Returns
+ * %true on success; %false on failure.
+ *
+ * Completion of percpu_ref_kill() in itself doesn't guarantee that tryget
+ * will fail.  For such guarantee, percpu_ref_kill_and_confirm() should be
+ * used.  After the confirm_kill callback is invoked, it's guaranteed that
+ * no new reference will be given out by percpu_ref_tryget().
+ */
+static inline bool percpu_ref_tryget(struct percpu_ref *ref)
+{
+	unsigned __percpu *pcpu_count;
+	int ret = false;
+
+	rcu_read_lock();
+
+	pcpu_count = ACCESS_ONCE(ref->pcpu_count);
+
+	if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) {
+		__this_cpu_inc(*pcpu_count);
+		ret = true;
+	}
+
+	rcu_read_unlock();
+
+	return ret;
+}
+
+/**
  * percpu_ref_put - decrement a percpu refcount
  * @ref: percpu_ref to put
  *