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Commit 91c63734 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
Browse files

kernel: cgroup: push rcu read locking from css_is_ancestor() to callsite 



Library functions should not grab locks when the callsites can do it,
even if the lock nests like the rcu read-side lock does.

Push the rcu_read_lock() from css_is_ancestor() to its single user,
mem_cgroup_same_or_subtree() in preparation for another user that may
already hold the rcu read-side lock.

Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0ce72d4f

kernel/cgroup.c

+10 −10
Original line number Diff line number Diff line
@@ -5132,7 +5132,7 @@ EXPORT_SYMBOL_GPL(css_depth); 
 * @root: the css supporsed to be an ancestor of the child.

 *

 * Returns true if "root" is an ancestor of "child" in its hierarchy. Because

 * this function reads css->id, this use rcu_dereference() and rcu_read_lock().

 * this function reads css->id, the caller must hold rcu_read_lock().

 * But, considering usual usage, the csses should be valid objects after test.

 * Assuming that the caller will do some action to the child if this returns

 * returns true, the caller must take "child";s reference count.
@@ -5144,18 +5144,18 @@ bool css_is_ancestor(struct cgroup_subsys_state *child, 
{

	struct css_id *child_id;

	struct css_id *root_id;

	bool ret = true;



	rcu_read_lock();

	child_id  = rcu_dereference(child->id);

	if (!child_id)

		return false;

	root_id = rcu_dereference(root->id);

	if (!child_id

	    || !root_id

	    || (child_id->depth < root_id->depth)

	    || (child_id->stack[root_id->depth] != root_id->id))

		ret = false;

	rcu_read_unlock();

	return ret;

	if (!root_id)

		return false;

	if (child_id->depth < root_id->depth)

		return false;

	if (child_id->stack[root_id->depth] != root_id->id)

		return false;

	return true;

}



void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)

mm/memcontrol.c

+9 −5
Original line number Diff line number Diff line
@@ -1152,12 +1152,16 @@ struct lruvec *mem_cgroup_lru_move_lists(struct zone *zone, 
static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,

		struct mem_cgroup *memcg)

{

	if (root_memcg != memcg) {

		return (root_memcg->use_hierarchy &&

			css_is_ancestor(&memcg->css, &root_memcg->css));

	}

	bool ret;



	if (root_memcg == memcg)

		return true;

	if (!root_memcg->use_hierarchy)

		return false;

	rcu_read_lock();

	ret = css_is_ancestor(&memcg->css, &root_memcg->css);

	rcu_read_unlock();

	return ret;

}



int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)