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| author | Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> | 2011-12-15 06:36:55 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2011-12-21 10:34:49 +0100 |
| commit | 4fc420c91f53e0a9f95665c6b14a1983716081e7 (patch) | |
| tree | e6bfad34810d368ed893780b9ddc05c5dbcb6923 /kernel/sched | |
| parent | sched: Remove cfs bandwidth period check in tg_set_cfs_period() (diff) | |
| download | linux-4fc420c91f53e0a9f95665c6b14a1983716081e7.tar.xz linux-4fc420c91f53e0a9f95665c6b14a1983716081e7.zip | |
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.c | 7 |
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); |