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Date: Tue, 17 Jun 2014 21:08:02 -0400
From: Tejun Heo <tj@...nel.org>
To: cl@...ux-foundation.org, kmo@...erainc.com
Cc: linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>
Subject: [PATCH 3/6] 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: Tejun Heo <tj@...nel.org>
Cc: Kent Overstreet <kmo@...erainc.com>
Cc: Christoph Lameter <cl@...ux-foundation.org>
---
include/linux/percpu-refcount.h | 35 +++++++++++++++++++++--------------
lib/percpu-refcount.c | 17 +++++++++--------
2 files changed, 30 insertions(+), 22 deletions(-)
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index bfdeb0d4..b62a4ee 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -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);
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 17bce2b..087f1a0 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -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 *)
--
1.9.3
--
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