sched: Fix cgroup movement of forking process
There is a small race between task_fork_fair() and sched_move_task(),
which is trying to move the parent.
task_fork_fair() sched_move_task()
--------------------------------+---------------------------------
cfs_rq = task_cfs_rq(current)
-> cfs_rq is the "old" one.
curr = cfs_rq->curr
-> curr is set to the parent.
task_rq_lock()
dequeue_task()
->parent.se.vruntime -= (old)cfs_rq->min_vruntime
enqueue_task()
->parent.se.vruntime += (new)cfs_rq->min_vruntime
task_rq_unlock()
raw_spin_lock_irqsave(rq->lock)
se->vruntime = curr->vruntime
-> vruntime of the child is set to that of the parent
which has already been updated by sched_move_task().
se->vruntime -= (old)cfs_rq->min_vruntime.
raw_spin_unlock_irqrestore(rq->lock)
As a result, vruntime of the child becomes far bigger than expected,
if (new)cfs_rq->min_vruntime >> (old)cfs_rq->min_vruntime.
This patch fixes this problem by setting "cfs_rq" and "curr" after
holding the rq->lock.
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/20111215143655.662676b0.nishimura@mxp.nes.nec.co.jp
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cea2fa8..525d69e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5190,8 +5190,8 @@
*/
static void task_fork_fair(struct task_struct *p)
{
- struct cfs_rq *cfs_rq = task_cfs_rq(current);
- struct sched_entity *se = &p->se, *curr = cfs_rq->curr;
+ struct cfs_rq *cfs_rq;
+ struct sched_entity *se = &p->se, *curr;
int this_cpu = smp_processor_id();
struct rq *rq = this_rq();
unsigned long flags;
@@ -5200,6 +5200,9 @@
update_rq_clock(rq);
+ cfs_rq = task_cfs_rq(current);
+ curr = cfs_rq->curr;
+
if (unlikely(task_cpu(p) != this_cpu)) {
rcu_read_lock();
__set_task_cpu(p, this_cpu);
