[PATCH -mmotm 2/8] memcg: move memcg_tasklist mutex

Daisuke Nishimura
2009-11-06T05:30:45Z

memcg_tasklist was introduced to serialize mem_cgroup_out_of_memory() and
mem_cgroup_move_task() to ensure tasks cannot be moved to another cgroup
during select_bad_process().

task_in_mem_cgroup(), which can be called by select_bad_process(), will check
whether a task is in the mem_cgroup or not by dereferencing task->cgroups
->subsys[]. So, it would be desirable to change task->cgroups
(rcu_assign_pointer() in cgroup_attach_task() does it) with memcg_tasklist held.

Now that we can define cancel_attach(), we can safely release memcg_tasklist
on fail path even if we hold memcg_tasklist in can_attach(). So let's move
mutex_lock/unlock() of memcg_tasklist.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
mm/memcontrol.c | 22 ++++++++++++++++++++--
1 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4bd3451..d3b2ac0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3395,18 +3395,34 @@ static int mem_cgroup_populate(struct cgroup_subsys *ss,
return ret;
}

+static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
+ struct cgroup *cgroup,
+ struct task_struct *p,
+ bool threadgroup)
+{
+ mutex_lock(&memcg_tasklist);
+ return 0;
+}
+
+static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
+ struct cgroup *cgroup,
+ struct task_struct *p,
+ bool threadgroup)
+{
+ mutex_unlock(&memcg_tasklist);
+}
+
static void mem_cgroup_move_task(struct cgroup_subsys *ss,
struct cgroup *cont,
struct cgroup *old_cont,
struct task_struct *p,
bool threadgroup)
{
- mutex_lock(&memcg_tasklist);
+ mutex_unlock(&memcg_tasklist);
/*
* FIXME: It's better to move charges of this process from old
* memcg to new memcg. But it's just on TODO-List now.
*/
- mutex_unlock(&memcg_tasklist);
}

struct cgroup_subsys mem_cgroup_subsys = {
@@ -3416,6 +3432,8 @@ struct cgroup_subsys mem_cgroup_subsys = {
.pre_destroy = mem_cgroup_pre_destroy,
.destroy = mem_cgroup_destroy,
.populate = mem_cgroup_populate,
+ .can_attach = mem_cgroup_can_attach,
+ .cancel_attach = mem_cgroup_cancel_attach,
.attach = mem_cgroup_move_task,
.early_init = 0,
.use_id = 1,
--
1.5.6.1