[PATCH percpu/for-3.11 2/2] percpu-refcount: implement percpu_ref_cancel_init()

Tejun Heo
2013-06-13T03:52:40Z

Normally, percpu_ref_init() initializes and percpu_ref_kill*()
initiates destruction which completes asynchronously. The
asynchronous destruction can be problematic in init failure path where
the caller wants to destroy half-constructed object - distinguishing
half-constructed objects from the usual release method can be painful
for complex objects.

This patch implements percpu_ref_cancel_init() which synchronously
destroys the percpu_ref without invoking release. To avoid
unintentional misuses, the function requires the ref to have finished
percpu_ref_init() but never used and triggers WARN otherwise.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/percpu-refcount.h | 1 +
lib/percpu-refcount.c | 27 +++++++++++++++++++++++++++
2 files changed, 28 insertions(+)

--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -69,6 +69,7 @@ struct percpu_ref {

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_and_confirm(struct percpu_ref *ref,
percpu_ref_func_t *confirm_kill);

--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -54,6 +54,33 @@ int percpu_ref_init(struct percpu_ref *r
return 0;
}

+/**
+ * percpu_ref_cancel_init - cancel percpu_ref_init()
+ * @ref: percpu_ref to cancel init for
+ *
+ * Once a percpu_ref is initialized, its destruction is initiated by
+ * percpu_ref_kill*() and completes asynchronously, which can be painful to
+ * do when destroying a half-constructed object in init failure path.
+ *
+ * This function destroys @ref without invoking @ref->release and the
+ * memory area containing it can be freed immediately on return. To
+ * prevent accidental misuse, it's required that @ref has finished
+ * percpu_ref_init(), whether successful or not, but never used.
+ */
+void percpu_ref_cancel_init(struct percpu_ref *ref)
+{
+ unsigned __percpu *pcpu_count = ref->pcpu_count;
+ int cpu;
+
+ WARN_ON_ONCE(atomic_read(&ref->count) != 1 + PCPU_COUNT_BIAS);
+
+ if (pcpu_count) {
+ for_each_possible_cpu(cpu)
+ WARN_ON_ONCE(*per_cpu_ptr(pcpu_count, cpu));
+ free_percpu(ref->pcpu_count);
+ }
+}
+
static void percpu_ref_kill_rcu(struct rcu_head *rcu)
{
struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);