Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit bc497bd3 authored by Tejun Heo's avatar Tejun Heo
Browse files

percpu-refcount: implement percpu_ref_cancel_init() 



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.

v2: Explain the weird name and usage restriction in the function
    comment.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarKent Overstreet <koverstreet@google.com>
parent acac7883

include/linux/percpu-refcount.h

+1 −0
Original line number Diff line number Diff line
@@ -68,6 +68,7 @@ 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(struct percpu_ref *ref);



#define PCPU_STATUS_BITS	2

lib/percpu-refcount.c

+31 −0
Original line number Diff line number Diff line
@@ -54,6 +54,37 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release) 
	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.

 *

 * The weird name and usage restriction are to prevent people from using

 * this function by mistake for normal shutdown instead of

 * percpu_ref_kill().

 */

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);