[PATCH 2/9] percpu_ref: minor code and comment updates

Tejun Heo
2014-09-23T05:58:46Z

* Some comments became stale. Updated.
* percpu_ref_tryget() unnecessarily initializes @ret. Removed.
* A blank line removed from percpu_ref_kill_rcu().
* Explicit function name in a WARN format string replaced with __func__.
* WARN_ON() in percpu_ref_reinit() converted to WARN_ON_ONCE().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
---
include/linux/percpu-refcount.h | 25 ++++++++++++++++---------
lib/percpu-refcount.c | 14 ++++++--------
2 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index f015f13..d44b027 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -115,8 +115,10 @@ static inline bool __pcpu_ref_alive(struct percpu_ref *ref,
* percpu_ref_get - increment a percpu refcount
* @ref: percpu_ref to get
*
- * Analagous to atomic_inc().
- */
+ * Analagous to atomic_long_inc().
+ *
+ * This function is safe to call as long as @ref is between init and exit.
+ */
static inline void percpu_ref_get(struct percpu_ref *ref)
{
unsigned long __percpu *pcpu_count;
@@ -138,12 +140,12 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
* Increment a percpu refcount unless its count already reached zero.
* Returns %true on success; %false on failure.
*
- * The caller is responsible for ensuring that @ref stays accessible.
+ * This function is safe to call as long as @ref is between init and exit.
*/
static inline bool percpu_ref_tryget(struct percpu_ref *ref)
{
unsigned long __percpu *pcpu_count;
- int ret = false;
+ int ret;

rcu_read_lock_sched();

@@ -166,12 +168,13 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
* Increment a percpu refcount unless it has already been killed. Returns
* %true on success; %false on failure.
*
- * Completion of percpu_ref_kill() in itself doesn't guarantee that tryget
- * will fail. For such guarantee, percpu_ref_kill_and_confirm() should be
- * used. After the confirm_kill callback is invoked, it's guaranteed that
- * no new reference will be given out by percpu_ref_tryget().
+ * Completion of percpu_ref_kill() in itself doesn't guarantee that this
+ * function will fail. For such guarantee, percpu_ref_kill_and_confirm()
+ * should be used. After the confirm_kill callback is invoked, it's
+ * guaranteed that no new reference will be given out by
+ * percpu_ref_tryget_live().
*
- * The caller is responsible for ensuring that @ref stays accessible.
+ * This function is safe to call as long as @ref is between init and exit.
*/
static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
{
@@ -196,6 +199,8 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
*
* Decrement the refcount, and if 0, call the release function (which was passed
* to percpu_ref_init())
+ *
+ * This function is safe to call as long as @ref is between init and exit.
*/
static inline void percpu_ref_put(struct percpu_ref *ref)
{
@@ -216,6 +221,8 @@ static inline void percpu_ref_put(struct percpu_ref *ref)
* @ref: percpu_ref to test
*
* Returns %true if @ref reached zero.
+ *
+ * This function is safe to call as long as @ref is between init and exit.
*/
static inline bool percpu_ref_is_zero(struct percpu_ref *ref)
{
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 070dab5..8ef3f5c 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -108,7 +108,6 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
* reaching 0 before we add the percpu counts. But doing it at the same
* time is equivalent and saves us atomic operations:
*/
-
atomic_long_add((long)count - PCPU_COUNT_BIAS, &ref->count);

WARN_ONCE(atomic_long_read(&ref->count) <= 0,
@@ -120,8 +119,8 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
ref->confirm_kill(ref);

/*
- * Now we're in single atomic_t mode with a consistent refcount, so it's
- * safe to drop our initial ref:
+ * Now we're in single atomic_long_t mode with a consistent
+ * refcount, so it's safe to drop our initial ref:
*/
percpu_ref_put(ref);
}
@@ -134,8 +133,8 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
* Equivalent to percpu_ref_kill() but also schedules kill confirmation if
* @confirm_kill is not NULL. @confirm_kill, which may not block, will be
* called after @ref is seen as dead from all CPUs - all further
- * invocations of percpu_ref_tryget() will fail. See percpu_ref_tryget()
- * for more details.
+ * invocations of percpu_ref_tryget_live() will fail. See
+ * percpu_ref_tryget_live() for more details.
*
* Due to the way percpu_ref is implemented, @confirm_kill will be called
* after at least one full RCU grace period has passed but this is an
@@ -145,8 +144,7 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
percpu_ref_func_t *confirm_kill)
{
WARN_ONCE(ref->pcpu_count_ptr & PCPU_REF_DEAD,
- "percpu_ref_kill() called more than once on %pf!",
- ref->release);
+ "%s called more than once on %pf!", __func__, ref->release);

ref->pcpu_count_ptr |= PCPU_REF_DEAD;
ref->confirm_kill = confirm_kill;
@@ -172,7 +170,7 @@ void percpu_ref_reinit(struct percpu_ref *ref)
int cpu;

BUG_ON(!pcpu_count);
- WARN_ON(!percpu_ref_is_zero(ref));
+ WARN_ON_ONCE(!percpu_ref_is_zero(ref));

atomic_long_set(&ref->count, 1 + PCPU_COUNT_BIAS);

--
1.9.3