diff options
| author | KAMEZAWA Hiroyuki | 2010-05-11 14:06:59 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2010-05-11 17:33:42 -0700 |
| commit | 747388d78a0ae768fd82b55c4ed38aa646a72364 (patch) | |
| tree | 03efabf9761209cffef4e8da9b6989887f76428e | |
| parent | 7f0f15464185a92f9d8791ad231bcd7bf6df54e4 (diff) | |
memcg: fix css_is_ancestor() RCU locking
Some callers (in memcontrol.c) calls css_is_ancestor() without
rcu_read_lock. Because css_is_ancestor() has to access RCU protected
data, it should be under rcu_read_lock().
This makes css_is_ancestor() itself does safe access to RCU protected
area. (At least, "root" can have refcnt==0 if it's not an ancestor of
"child". So, we need rcu_read_lock().)
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | kernel/cgroup.c | 31 | ||||
| -rw-r--r-- | mm/memcontrol.c | 4 |
2 files changed, 26 insertions, 9 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 6db8b7f297a1..6d870f2d1228 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4464,15 +4464,36 @@ unsigned short css_depth(struct cgroup_subsys_state *css) } EXPORT_SYMBOL_GPL(css_depth); +/** + * css_is_ancestor - test "root" css is an ancestor of "child" + * @child: the css to be tested. + * @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(). + * 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. + * If "child" is valid object and this returns true, "root" is valid, too. + */ + bool css_is_ancestor(struct cgroup_subsys_state *child, const struct cgroup_subsys_state *root) { - struct css_id *child_id = rcu_dereference(child->id); - struct css_id *root_id = rcu_dereference(root->id); + struct css_id *child_id; + struct css_id *root_id; + bool ret = true; - if (!child_id || !root_id || (child_id->depth < root_id->depth)) - return false; - return child_id->stack[root_id->depth] == root_id->id; + rcu_read_lock(); + child_id = rcu_dereference(child->id); + 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; } static void __free_css_id_cb(struct rcu_head *head) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 595d03f33b2c..8a79a6f0f029 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -811,12 +811,10 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem) * enabled in "curr" and "curr" is a child of "mem" in *cgroup* * hierarchy(even if use_hierarchy is disabled in "mem"). */ - rcu_read_lock(); if (mem->use_hierarchy) ret = css_is_ancestor(&curr->css, &mem->css); else ret = (curr == mem); - rcu_read_unlock(); css_put(&curr->css); return ret; } @@ -1603,7 +1601,6 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, * There is a small race that "from" or "to" can be * freed by rmdir, so we use css_tryget(). */ - rcu_read_lock(); from = mc.from; to = mc.to; if (from && css_tryget(&from->css)) { @@ -1624,7 +1621,6 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, do_continue = (to == mem_over_limit); css_put(&to->css); } - rcu_read_unlock(); if (do_continue) { DEFINE_WAIT(wait); prepare_to_wait(&mc.waitq, &wait, |