Messages in this thread Patch in this message | | | From | Johannes Weiner <> | Subject | [patch 1/2] kernel: cgroup: push rcu read locking from css_is_ancestor() to callsite | Date | Tue, 28 Feb 2012 15:14:48 +0100 |
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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> --- kernel/cgroup.c | 20 ++++++++++---------- mm/memcontrol.c | 14 +++++++++----- 2 files changed, 19 insertions(+), 15 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 4be474d..9003bd8 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4841,7 +4841,7 @@ 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. @@ -4853,18 +4853,18 @@ 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) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e4be95a..b4622fb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1047,12 +1047,16 @@ 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; - 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) -- 1.7.7.6
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