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authorTejun Heo <tj@kernel.org>2014-05-16 21:22:52 +0400
committerTejun Heo <tj@kernel.org>2014-05-16 21:22:52 +0400
commit6f4524d355a86769b65d5420a6ef47fb0bba9b72 (patch)
treeb0edfe7bfc0a20173041aa8811acf4629ccb020d /include/linux/cgroup.h
parent7a3bb24f7c5ceebad19b12b66fd832a27a7e90df (diff)
downloadlinux-6f4524d355a86769b65d5420a6ef47fb0bba9b72.tar.xz
cgroup: implement css_tryget()
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. v2: Take the new flag CSS_NO_REF into account. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Johannes Weiner <hannes@cmpxchg.org>
Diffstat (limited to 'include/linux/cgroup.h')
-rw-r--r--include/linux/cgroup.h18
1 files changed, 18 insertions, 0 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b76999954beb..4afe544d3547 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -113,6 +113,24 @@ 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)
+{
+ if (!(css->flags & CSS_NO_REF))
+ return percpu_ref_tryget(&css->refcnt);
+ return true;
+}
+
+/**
* css_tryget_online - try to obtain a reference on the specified css if online
* @css: target css
*