percpu_ref: rename things to prepare for decoupling percpu/atomic mode switch

percpu_ref will be restructured so that percpu/atomic mode switching
and reference killing are dedoupled.  In preparation, do the following
renames.

* percpu_ref->confirm_kill	-> percpu_ref->confirm_switch
* __PERCPU_REF_DEAD		-> __PERCPU_REF_ATOMIC
* __percpu_ref_alive()		-> __ref_is_percpu()

This patch is pure rename and doesn't introduce any functional
changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Kent Overstreet <kmo@daterainc.com>

include/linux/percpu-refcount.h

@@ -54,6 +54,11 @@
 struct percpu_ref;
 typedef void (percpu_ref_func_t)(struct percpu_ref *);
 
+/* flags set in the lower bits of percpu_ref->percpu_count_ptr */
+enum {
+	__PERCPU_REF_ATOMIC	= 1LU << 0,	/* operating in atomic mode */
+};
+
 struct percpu_ref {
 	atomic_long_t		count;
 	/*
@@ -62,7 +67,7 @@ struct percpu_ref {
 	 */
 	unsigned long		percpu_count_ptr;
 	percpu_ref_func_t	*release;
-	percpu_ref_func_t	*confirm_kill;
+	percpu_ref_func_t	*confirm_switch;
 	struct rcu_head		rcu;
 };
 
@@ -88,23 +93,21 @@ static inline void percpu_ref_kill(struct percpu_ref *ref)
 	return percpu_ref_kill_and_confirm(ref, NULL);
 }
 
-#define __PERCPU_REF_DEAD	1
-
 /*
  * Internal helper.  Don't use outside percpu-refcount proper.  The
  * function doesn't return the pointer and let the caller test it for NULL
  * because doing so forces the compiler to generate two conditional
  * branches as it can't assume that @ref->percpu_count is not NULL.
  */
-static inline bool __percpu_ref_alive(struct percpu_ref *ref,
+static inline bool __ref_is_percpu(struct percpu_ref *ref,
-				      unsigned long __percpu **percpu_countp)
+					  unsigned long __percpu **percpu_countp)
 {
 	unsigned long percpu_ptr = ACCESS_ONCE(ref->percpu_count_ptr);
 
 	/* paired with smp_store_release() in percpu_ref_reinit() */
 	smp_read_barrier_depends();
 
-	if (unlikely(percpu_ptr & __PERCPU_REF_DEAD))
+	if (unlikely(percpu_ptr & __PERCPU_REF_ATOMIC))
 		return false;
 
 	*percpu_countp = (unsigned long __percpu *)percpu_ptr;
@@ -125,7 +128,7 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
 
 	rcu_read_lock_sched();
 
-	if (__percpu_ref_alive(ref, &percpu_count))
+	if (__ref_is_percpu(ref, &percpu_count))
 		this_cpu_inc(*percpu_count);
 	else
 		atomic_long_inc(&ref->count);
@@ -149,7 +152,7 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
 
 	rcu_read_lock_sched();
 
-	if (__percpu_ref_alive(ref, &percpu_count)) {
+	if (__ref_is_percpu(ref, &percpu_count)) {
 		this_cpu_inc(*percpu_count);
 		ret = true;
 	} else {
@@ -183,7 +186,7 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
 
 	rcu_read_lock_sched();
 
-	if (__percpu_ref_alive(ref, &percpu_count)) {
+	if (__ref_is_percpu(ref, &percpu_count)) {
 		this_cpu_inc(*percpu_count);
 		ret = true;
 	}
@@ -208,7 +211,7 @@ static inline void percpu_ref_put(struct percpu_ref *ref)
 
 	rcu_read_lock_sched();
 
-	if (__percpu_ref_alive(ref, &percpu_count))
+	if (__ref_is_percpu(ref, &percpu_count))
 		this_cpu_dec(*percpu_count);
 	else if (unlikely(atomic_long_dec_and_test(&ref->count)))
 		ref->release(ref);
@@ -228,7 +231,7 @@ static inline bool percpu_ref_is_zero(struct percpu_ref *ref)
 {
 	unsigned long __percpu *percpu_count;
 
-	if (__percpu_ref_alive(ref, &percpu_count))
+	if (__ref_is_percpu(ref, &percpu_count))
 		return false;
 	return !atomic_long_read(&ref->count);
 }

lib/percpu-refcount.c

@@ -34,7 +34,7 @@
 static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
 {
 	return (unsigned long __percpu *)
-		(ref->percpu_count_ptr & ~__PERCPU_REF_DEAD);
+		(ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
 }
 
 /**
@@ -80,7 +80,7 @@ void percpu_ref_exit(struct percpu_ref *ref)
 
 	if (percpu_count) {
 		free_percpu(percpu_count);
-		ref->percpu_count_ptr = __PERCPU_REF_DEAD;
+		ref->percpu_count_ptr = __PERCPU_REF_ATOMIC;
 	}
 }
 EXPORT_SYMBOL_GPL(percpu_ref_exit);
@@ -117,8 +117,8 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
 		  ref->release, atomic_long_read(&ref->count));
 
 	/* @ref is viewed as dead on all CPUs, send out kill confirmation */
-	if (ref->confirm_kill)
+	if (ref->confirm_switch)
-		ref->confirm_kill(ref);
+		ref->confirm_switch(ref);
 
 	/*
 	 * Now we're in single atomic_long_t mode with a consistent
@@ -145,11 +145,11 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
 void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
 				 percpu_ref_func_t *confirm_kill)
 {
-	WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_DEAD,
+	WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC,
 		  "%s called more than once on %pf!", __func__, ref->release);
 
-	ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
+	ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
-	ref->confirm_kill = confirm_kill;
+	ref->confirm_switch = confirm_kill;
 
 	call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);
 }
@@ -178,14 +178,14 @@ void percpu_ref_reinit(struct percpu_ref *ref)
 
 	/*
 	 * Restore per-cpu operation.  smp_store_release() is paired with
-	 * smp_read_barrier_depends() in __percpu_ref_alive() and
+	 * smp_read_barrier_depends() in __ref_is_percpu() and guarantees
-	 * guarantees that the zeroing is visible to all percpu accesses
+	 * that the zeroing is visible to all percpu accesses which can see
-	 * which can see the following __PERCPU_REF_DEAD clearing.
+	 * the following __PERCPU_REF_ATOMIC clearing.
 	 */
 	for_each_possible_cpu(cpu)
 		*per_cpu_ptr(percpu_count, cpu) = 0;
 
 	smp_store_release(&ref->percpu_count_ptr,
-			  ref->percpu_count_ptr & ~__PERCPU_REF_DEAD);
+			  ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_reinit);