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Commit eae7975d authored by Tejun Heo's avatar Tejun Heo
Browse files

percpu-refcount: add helpers for ->percpu_count accesses 



* All four percpu_ref_*() operations implemented in the header file
  perform the same operation to determine whether the percpu_ref is
  alive and extract the percpu pointer.  Factor out the common logic
  into __pcpu_ref_alive().  This doesn't change the generated code.

* There are a couple places in percpu-refcount.c which masks out
  PCPU_REF_DEAD to obtain the percpu pointer.  Factor it out into
  pcpu_count_ptr().

* The above changes make the WARN_ON_ONCE() conditional at the top of
  percpu_ref_kill_and_confirm() the only user of REF_STATUS().  Test
  PCPU_REF_DEAD directly and remove REF_STATUS().

This patch doesn't introduce any functional change.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
parent d630dc4c

include/linux/percpu-refcount.h

+21 −14
Original line number Diff line number Diff line
@@ -88,10 +88,25 @@ static inline void percpu_ref_kill(struct percpu_ref *ref) 
	return percpu_ref_kill_and_confirm(ref, NULL);

}



#define PCPU_REF_PTR		0

#define PCPU_REF_DEAD		1



#define REF_STATUS(count)	(((unsigned long) count) & PCPU_REF_DEAD)

/*

 * 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->pcpu_count is not NULL.

 */

static inline bool __pcpu_ref_alive(struct percpu_ref *ref,

				    unsigned __percpu **pcpu_countp)

{

	unsigned long pcpu_ptr = (unsigned long)ACCESS_ONCE(ref->pcpu_count);



	if (unlikely(pcpu_ptr & PCPU_REF_DEAD))

		return false;



	*pcpu_countp = (unsigned __percpu *)pcpu_ptr;

	return true;

}



/**

 * percpu_ref_get - increment a percpu refcount
@@ -105,9 +120,7 @@ static inline void percpu_ref_get(struct percpu_ref *ref) 


	rcu_read_lock_sched();



	pcpu_count = ACCESS_ONCE(ref->pcpu_count);



	if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR))

	if (__pcpu_ref_alive(ref, &pcpu_count))

		this_cpu_inc(*pcpu_count);

	else

		atomic_inc(&ref->count);
@@ -131,9 +144,7 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) 


	rcu_read_lock_sched();



	pcpu_count = ACCESS_ONCE(ref->pcpu_count);



	if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) {

	if (__pcpu_ref_alive(ref, &pcpu_count)) {

		this_cpu_inc(*pcpu_count);

		ret = true;

	} else {
@@ -166,9 +177,7 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref) 


	rcu_read_lock_sched();



	pcpu_count = ACCESS_ONCE(ref->pcpu_count);



	if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) {

	if (__pcpu_ref_alive(ref, &pcpu_count)) {

		this_cpu_inc(*pcpu_count);

		ret = true;

	}
@@ -191,9 +200,7 @@ static inline void percpu_ref_put(struct percpu_ref *ref) 


	rcu_read_lock_sched();



	pcpu_count = ACCESS_ONCE(ref->pcpu_count);



	if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR))

	if (__pcpu_ref_alive(ref, &pcpu_count))

		this_cpu_dec(*pcpu_count);

	else if (unlikely(atomic_dec_and_test(&ref->count)))

		ref->release(ref);

lib/percpu-refcount.c

+9 −8
Original line number Diff line number Diff line
@@ -31,6 +31,11 @@ 


#define PCPU_COUNT_BIAS		(1U << 31)



static unsigned __percpu *pcpu_count_ptr(struct percpu_ref *ref)

{

	return (unsigned __percpu *)((unsigned long)ref->pcpu_count & ~PCPU_REF_DEAD);

}



/**

 * percpu_ref_init - initialize a percpu refcount

 * @ref: percpu_ref to initialize
@@ -74,7 +79,7 @@ EXPORT_SYMBOL_GPL(percpu_ref_init); 
 */

void percpu_ref_cancel_init(struct percpu_ref *ref)

{

	unsigned __percpu *pcpu_count = ref->pcpu_count;

	unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);

	int cpu;



	WARN_ON_ONCE(atomic_read(&ref->count) != 1 + PCPU_COUNT_BIAS);
@@ -82,7 +87,7 @@ void percpu_ref_cancel_init(struct percpu_ref *ref) 
	if (pcpu_count) {

		for_each_possible_cpu(cpu)

			WARN_ON_ONCE(*per_cpu_ptr(pcpu_count, cpu));

		free_percpu(ref->pcpu_count);

		free_percpu(pcpu_count);

	}

}

EXPORT_SYMBOL_GPL(percpu_ref_cancel_init);
@@ -90,14 +95,10 @@ EXPORT_SYMBOL_GPL(percpu_ref_cancel_init); 
static void percpu_ref_kill_rcu(struct rcu_head *rcu)

{

	struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);

	unsigned __percpu *pcpu_count = ref->pcpu_count;

	unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);

	unsigned count = 0;

	int cpu;



	/* Mask out PCPU_REF_DEAD */

	pcpu_count = (unsigned __percpu *)

		(((unsigned long) pcpu_count) & ~PCPU_REF_DEAD);



	for_each_possible_cpu(cpu)

		count += *per_cpu_ptr(pcpu_count, cpu);
@@ -152,7 +153,7 @@ 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_STATUS(ref->pcpu_count) == PCPU_REF_DEAD,

	WARN_ONCE((unsigned long)ref->pcpu_count & PCPU_REF_DEAD,

		  "percpu_ref_kill() called more than once!\n");



	ref->pcpu_count = (unsigned __percpu *)