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: Tejun Heo <tj@kernel.org>
Acked-by: Kent Overstreet <koverstreet@google.com>
This commit is contained in:
Tejun Heo 2013-06-12 20:52:35 -07:00
Родитель acac7883ee
Коммит bc497bd33b
2 изменённых файлов: 32 добавлений и 0 удалений

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@ -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

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@ -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);