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authorKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>2010-05-11 14:06:59 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-11 17:33:42 -0700
commit747388d78a0ae768fd82b55c4ed38aa646a72364 (patch)
tree03efabf9761209cffef4e8da9b6989887f76428e /kernel
parent7f0f15464185a92f9d8791ad231bcd7bf6df54e4 (diff)
downloadlinux-2.6.34-ux500-747388d78a0ae768fd82b55c4ed38aa646a72364.tar.gz
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup.c31
1 files changed, 26 insertions, 5 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 6db8b7f297a..6d870f2d122 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)