diff options
| author | Johannes Weiner <hannes@cmpxchg.org> | 2012-05-30 00:06:24 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-05-30 01:22:20 +0200 |
| commit | 91c63734f6908425903aed69c04035592f18d398 (patch) | |
| tree | 6790827ab915b17c63d5c39d8c72c47f3764f868 /kernel | |
| parent | mm: do_migrate_pages(): rename arguments (diff) | |
| download | linux-91c63734f6908425903aed69c04035592f18d398.tar.xz linux-91c63734f6908425903aed69c04035592f18d398.zip | |
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/cgroup.c | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index a0c6af34d500..0f3527d6184a 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -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) |