From 6f4524d355a86769b65d5420a6ef47fb0bba9b72 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 16 May 2014 13:22:52 -0400 Subject: [PATCH] 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 Acked-by: Li Zefan Cc: Johannes Weiner --- include/linux/cgroup.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) 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 @@ -112,6 +112,24 @@ static inline void css_get(struct cgroup_subsys_state *css) percpu_ref_get(&css->refcnt); } +/** + * 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 -- 2.39.5