[PATCH 4/4] percpu_ref: release percpu memory early without PERCPU_REF_ALLOW_REINIT

[Roman Gushchin <guro@fb.com>]

Release percpu memory after finishing the switch to the atomic mode
if only PERCPU_REF_ALLOW_REINIT isn't set.

Signed-off-by: Roman Gushchin <guro@fb.com>
---
 include/linux/percpu-refcount.h |  1 +
 lib/percpu-refcount.c           | 13 +++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 0f0240af8520..7aef0abc194a 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -102,6 +102,7 @@ struct percpu_ref {
 	percpu_ref_func_t	*release;
 	percpu_ref_func_t	*confirm_switch;
 	bool			force_atomic:1;
+	bool			allow_reinit:1;
 	struct rcu_head		rcu;
 };
 
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index da54318d3b55..47f0aeb136c4 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -69,11 +69,14 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
 		return -ENOMEM;
 
 	ref->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
+	ref->allow_reinit = flags & PERCPU_REF_ALLOW_REINIT;
 
-	if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD))
+	if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD)) {
 		ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
-	else
+		ref->allow_reinit = true;
+	} else {
 		start_count += PERCPU_COUNT_BIAS;
+	}
 
 	if (flags & PERCPU_REF_INIT_DEAD)
 		ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
@@ -119,6 +122,9 @@ static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
 	ref->confirm_switch = NULL;
 	wake_up_all(&percpu_ref_switch_waitq);
 
+	if (!ref->allow_reinit)
+		percpu_ref_exit(ref);
+
 	/* drop ref from percpu_ref_switch_to_atomic() */
 	percpu_ref_put(ref);
 }
@@ -194,6 +200,9 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
 	if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))
 		return;
 
+	if (WARN_ON_ONCE(!ref->allow_reinit))
+		return;
+
 	atomic_long_add(PERCPU_COUNT_BIAS, &ref->count);
 
 	/*
-- 
2.20.1