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Commit 6f4524d3 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
parent 7a3bb24f

include/linux/cgroup.h

+18 −0
Original line number Diff line number Diff line
@@ -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