From eae7975ddf031b3084f4a5f7d88f698aefad96fb Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sat, 28 Jun 2014 08:10:13 -0400 Subject: 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 Cc: Kent Overstreet Cc: Christoph Lameter --- include/linux/percpu-refcount.h | 35 +++++++++++++++++++++-------------- 1 file changed, 21 insertions(+), 14 deletions(-) (limited to 'include/linux/percpu-refcount.h') diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index bfdeb0d48e21..b62a4ee6d6ad 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); -- cgit v1.2.3-59-g8ed1b