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authorTejun Heo <tj@kernel.org>2014-05-09 23:11:53 +0400
committerTejun Heo <tj@kernel.org>2014-05-09 23:42:35 +0400
commit4fb6e25049cb6fa0accc7f1b7c192b952fad7ac8 (patch)
tree6be13f79be6f0bb6dc51ca10431c9737af8aee92 /include/linux/percpu-refcount.h
parent2070d50e1cbe3d7f157cbf8e63279c893f375d7f (diff)
downloadlinux-4fb6e25049cb6fa0accc7f1b7c192b952fad7ac8.tar.xz
percpu-refcount: implement percpu_ref_tryget()
Implement percpu_ref_tryget() which fails if the refcnt already reached zero. Note that this is different from the recently renamed percpu_ref_tryget_live() which fails if the refcnt has been killed and is draining the remaining references. percpu_ref_tryget() succeeds on a killed refcnt as long as its current refcnt is above zero. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Kent Overstreet <kmo@daterainc.com>
Diffstat (limited to 'include/linux/percpu-refcount.h')
-rw-r--r--include/linux/percpu-refcount.h32
1 files changed, 32 insertions, 0 deletions
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index e22d15597cc3..dba35c411e8c 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -118,6 +118,36 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
}
/**
+ * percpu_ref_tryget - try to increment a percpu refcount
+ * @ref: percpu_ref to try-get
+ *
+ * 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.
+ */
+static inline bool percpu_ref_tryget(struct percpu_ref *ref)
+{
+ unsigned __percpu *pcpu_count;
+ int ret = false;
+
+ rcu_read_lock_sched();
+
+ pcpu_count = ACCESS_ONCE(ref->pcpu_count);
+
+ if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) {
+ __this_cpu_inc(*pcpu_count);
+ ret = true;
+ } else {
+ ret = atomic_inc_not_zero(&ref->count);
+ }
+
+ rcu_read_unlock_sched();
+
+ return ret;
+}
+
+/**
* percpu_ref_tryget_live - try to increment a live percpu refcount
* @ref: percpu_ref to try-get
*
@@ -128,6 +158,8 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
* 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().
+ *
+ * The caller is responsible for ensuring that @ref stays accessible.
*/
static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
{