From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Now, for checking a memcg is under task-account-moving, we do css_tryget()
against mc.to and mc.from. But this ust complicates things. This patch
makes the check easier. (And I doubt the current code has some races..)
This patch adds a spinlock to move_charge_struct and guard modification
of mc.to and mc.from. By this, we don't have to think about complicated
races around this not-critical path.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
mm/memcontrol.c | 48 ++++++++++++++++++++++++++++--------------------
1 file changed, 28 insertions(+), 20 deletions(-)
Index: mmotm-2.6.34-May21/mm/memcontrol.c
===================================================================
--- mmotm-2.6.34-May21.orig/mm/memcontrol.c
+++ mmotm-2.6.34-May21/mm/memcontrol.c
@@ -268,6 +268,7 @@ enum move_type {
/* "mc" and its members are protected by cgroup_mutex */
static struct move_charge_struct {
+ spinlock_t lock; /* for from, to, moving_task */
struct mem_cgroup *from;
struct mem_cgroup *to;
unsigned long precharge;
@@ -276,6 +277,7 @@ static struct move_charge_struct {
struct task_struct *moving_task; /* a task moving charges */
wait_queue_head_t waitq; /* a waitq for other context */
} mc = {
+ .lock = __SPIN_LOCK_UNLOCKED(mc.lock),
.waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
};
@@ -1076,26 +1078,25 @@ static unsigned int get_swappiness(struc
static bool mem_cgroup_under_move(struct mem_cgroup *mem)
{
- struct mem_cgroup *from = mc.from;
- struct mem_cgroup *to = mc.to;
+ struct mem_cgroup *from;
+ struct mem_cgroup *to;
bool ret = false;
-
- if (from == mem || to == mem)
- return true;
-
- if (!from || !to || !mem->use_hierarchy)
- return false;
-
- rcu_read_lock();
- if (css_tryget(&from->css)) {
- ret = css_is_ancestor(&from->css, &mem->css);
- css_put(&from->css);
- }
- if (!ret && css_tryget(&to->css)) {
- ret = css_is_ancestor(&to->css, &mem->css);
+ /*
+ * Unlike task_move routines, we access mc.to, mc.from not under
+ * mutual execution by cgroup_mutex. Here, we take spinlock instead.
+ */
+ spin_lock_irq(&mc.lock);
+ from = mc.from;
+ to = mc.to;
+ if (!from)
+ goto unlock;
+ if (from == mem || to == mem
+ || (mem->use_hierarchy && css_is_ancestor(&from->css, &mem->css))
+ || (mem->use_hierarchy && css_is_ancestor(&to->css, &mem->css)))
css_put(&to->css);
- }
- rcu_read_unlock();
+ ret = true;
+unlock:
+ spin_unlock_irq(&mc.lock);
return ret;
}
@@ -4444,11 +4445,13 @@ static int mem_cgroup_precharge_mc(struc
static void mem_cgroup_clear_mc(void)
{
+ struct mem_cgroup *from = mc.from;
+ struct mem_cgroup *to = mc.to;
+
/* we must uncharge all the leftover precharges from mc.to */
if (mc.precharge) {
__mem_cgroup_cancel_charge(mc.to, mc.precharge);
mc.precharge = 0;
- memcg_oom_recover(mc.to);
}
/*
* we didn't uncharge from mc.from at mem_cgroup_move_account(), so
@@ -4457,7 +4460,6 @@ static void mem_cgroup_clear_mc(void)
if (mc.moved_charge) {
__mem_cgroup_cancel_charge(mc.from, mc.moved_charge);
mc.moved_charge = 0;
- memcg_oom_recover(mc.from);
}
/* we must fixup refcnts and charges */
if (mc.moved_swap) {
@@ -4482,9 +4484,13 @@ static void mem_cgroup_clear_mc(void)
mc.moved_swap = 0;
}
+ spin_lock_irq(&mc.lock);
mc.from = NULL;
mc.to = NULL;
mc.moving_task = NULL;
+ spin_unlock_irq(&mc.lock);
+ memcg_oom_recover(from);
+ memcg_oom_recover(to);
wake_up_all(&mc.waitq);
}
@@ -4513,12 +4519,14 @@ static int mem_cgroup_can_attach(struct
VM_BUG_ON(mc.moved_charge);
VM_BUG_ON(mc.moved_swap);
VM_BUG_ON(mc.moving_task);
+ spin_lock_irq(&mc.lock);
mc.from = from;
mc.to = mem;
mc.precharge = 0;
mc.moved_charge = 0;
mc.moved_swap = 0;
mc.moving_task = current;
+ spin_unlock_irq(&mc.lock);
ret = mem_cgroup_precharge_mc(mm);
if (ret)
--
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