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@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
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 @@
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 @@
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 @@
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 @@
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 @@
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);