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@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> --- 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 -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html