[PATCH 4/6] Changes css_set freeing mechanism to be under RCU

Ben Blum
2009-07-31T01:52:13Z

Changes css_set freeing mechanism to be under RCU

This is a prepatch for making the procs file writable. In order to free the
old css_sets for each task to be moved as they're being moved, the freeing
mechanism must be RCU-protected, or else we would have to have a call to
synchronize_rcu() for each task before freeing its old css_set.

Signed-off-by: Ben Blum <bblum@google.com>

---

include/linux/cgroup.h | 3 +++
kernel/cgroup.c | 8 +++++++-
2 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b934b72..24e3f1a 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -260,6 +260,9 @@ struct css_set {
* during subsystem registration (at boot time).
*/
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
+
+ /* For RCU-protected deletion */
+ struct rcu_head rcu_head;
};

/*
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f6d5969..a12bc8e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -288,6 +288,12 @@ static void unlink_css_set(struct css_set *cg)
}
}

+static void free_css_set_rcu(struct rcu_head *obj)
+{
+ struct css_set *cg = container_of(obj, struct css_set, rcu_head);
+ kfree(cg);
+}
+
static void __put_css_set(struct css_set *cg, int taskexit)
{
int i;
@@ -317,7 +323,7 @@ static void __put_css_set(struct css_set *cg, int taskexit)
}
}
rcu_read_unlock();
- kfree(cg);
+ call_rcu(&cg->rcu_head, free_css_set_rcu);
}

/*