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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: Johannes Weiner <hannes@cmpxchg.org>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2012-05-29 15:06:24 -07:00 committed by Linus Torvalds
parent 0ce72d4f73
commit 91c63734f6
2 changed files with 19 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
kernel/cgroup.c
View File

@ -5132,7 +5132,7 @@ EXPORT_SYMBOL_GPL(css_depth);
* @root: the css supporsed to be an ancestor of the child. * @root: the css supporsed to be an ancestor of the child.
* *
* Returns true if "root" is an ancestor of "child" in its hierarchy. Because * 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. * 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 * Assuming that the caller will do some action to the child if this returns
* returns true, the caller must take "child";s reference count. * 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 *child_id;
struct css_id *root_id; struct css_id *root_id;
bool ret = true;
rcu_read_lock();
child_id = rcu_dereference(child->id); child_id = rcu_dereference(child->id);
if (!child_id)
return false;
root_id = rcu_dereference(root->id); root_id = rcu_dereference(root->id);
if (!child_id if (!root_id)
|| !root_id return false;
|| (child_id->depth < root_id->depth) if (child_id->depth < root_id->depth)
|| (child_id->stack[root_id->depth] != root_id->id)) return false;
ret = false; if (child_id->stack[root_id->depth] != root_id->id)
rcu_read_unlock(); return false;
return ret; return true;
} }
void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css) void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)

14
mm/memcontrol.c
View File

@ -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, static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
struct mem_cgroup *memcg) struct mem_cgroup *memcg)
{ {
if (root_memcg != memcg) { bool ret;
return (root_memcg->use_hierarchy &&
css_is_ancestor(&memcg->css, &root_memcg->css));
}
return true; 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) int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)