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authorDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>2011-12-15 14:36:55 +0900
committerIngo Molnar <mingo@elte.hu>2011-12-21 10:34:49 +0100
commit4fc420c91f53e0a9f95665c6b14a1983716081e7 (patch)
treee6bfad34810d368ed893780b9ddc05c5dbcb6923 /kernel/sched
parent11534ec5b6cea13ae38d31799d2a5290c5d724af (diff)
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>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/fair.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cea2fa853274..525d69e5fb78 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5190,8 +5190,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
*/
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 @@ static void task_fork_fair(struct task_struct *p)
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);