[PATCH 14/14] cgroup: implement css_tryget()

Tejun Heo
2014-05-09T21:32:03Z

Implement css_tryget() which tries to grab a cgroup_subsys_state's
reference as long as it already hasn't reached zero. Combined with
the recent css iterator changes to include offline && !released csses
during traversal, this can be used to access csses regardless of its
online state.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
---
include/linux/cgroup.h | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c8eb66e..6dd3867 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -111,6 +111,22 @@ static inline void css_get(struct cgroup_subsys_state *css)
}

/**
+ * css_tryget - try to obtain a reference on the specified css
+ * @css: target css
+ *
+ * Obtain a reference on @css unless it already has reached zero and is
+ * being released. This function doesn't care whether @css is on or
+ * offline. The caller naturally needs to ensure that @css is accessible
+ * but doesn't have to be holding a reference on it - IOW, RCU protected
+ * access is good enough for this function. Returns %true if a reference
+ * count was successfully obtained; %false otherwise.
+ */
+static inline bool css_tryget(struct cgroup_subsys_state *css)
+{
+ return percpu_ref_tryget(&css->refcnt);
+}
+
+/**
* css_tryget_online - try to obtain a reference on the specified css if online
* @css: target css
*
--
1.9.0