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Date: Mon, 16 May 2011 21:37:48 +0800
From: Yong Zhang <yong.zhang0@...il.com>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Oleg Nesterov <oleg@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...e.hu>, Li Zefan <lizf@...fujitsu.com>,
Miao Xie <miaox@...fujitsu.com>
Subject: Re: [PATCH 1/2] cpuset: fix cpuset_cpus_allowed_fallback() don't
update tsk->rt.nr_cpus_allowed
On Fri, May 13, 2011 at 07:02:15PM +0200, Peter Zijlstra wrote:
> On Fri, 2011-05-13 at 14:42 +0800, Yong Zhang wrote:
> > > - rcu_cpu_kthread_should_stop() call set_cpus_allowed_ptr() again
> > > periodically.
> > > then, it can reset cpumask if cpuset_cpus_allowed_fallback() change it.
> > > my debug print obseve following cpumask change occur at boot time.
> > > 1) kthread_bind: bind cpu1
> > > 2) cpuset_cpus_allowed_fallback: bind possible cpu
> > > 3) rcu_cpu_kthread_should_stop: rebind cpu1
> > > - while tsk->rt.nr_cpus_allowed == 1, sched load balancer never be crash.
> >
> > Seems rcu_spawn_one_cpu_kthread() call wake_up_process() directly,
> > which is under hotplug event CPU_UP_PREPARE. Maybe it should be
> > under CPU_ONLINE.
>
> IIRC I talked to Paul about this a while back and ONLINE is too late,
> however STARTING should work. At the time he couldn't quite get that to
> work, but the above situation is indeed the root cause of our problems.
>
> We shouldn't try to run a cpu affine thread before the cpu in question
> is actually able to run stuff.
But I'm afraid this patch still doesn't help.
If I understand your patch correctly, you just put the wake up to CPU_STARTING,
but it's still before CPU_ONLINE.
Please check my mail to Paul's in this thread group.
Thanks,
Yong
>
> I did me a little hackery and with the below patch my kernel still
> boots...
>
> Would that sort your issue?
>
> ---
> kernel/rcutree.c | 44 ++++++++++++++++++++++++++++++++++++++------
> kernel/rcutree_plugin.h | 1 -
> 2 files changed, 38 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 5616b17..e0218ed 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1656,7 +1656,6 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
> per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
> WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
> per_cpu(rcu_cpu_kthread_task, cpu) = t;
> - wake_up_process(t);
> sp.sched_priority = RCU_KTHREAD_PRIO;
> sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> return 0;
> @@ -1764,13 +1763,33 @@ static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
> raw_spin_lock_irqsave(&rnp->lock, flags);
> rnp->node_kthread_task = t;
> raw_spin_unlock_irqrestore(&rnp->lock, flags);
> - wake_up_process(t);
> sp.sched_priority = 99;
> sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> }
> return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
> }
>
> +static void __cpuinit rcu_wake_cpu_kthread(int cpu)
> +{
> + struct task_struct *p = per_cpu(rcu_cpu_kthread_task, cpu);
> +
> + if (p)
> + wake_up_process(p);
> +}
> +
> +static void __cpuinit rcu_wake_node_kthread(struct rcu_node *rnp)
> +{
> + if (!rnp)
> + return;
> +
> + if (rnp->node_kthread_task)
> + wake_up_process(rnp->node_kthread_task);
> +#ifdef CONFIG_RCU_BOOST
> + if (rnp->boost_kthread_task)
> + wake_up_process(rnp->boost_kthread_task);
> +#endif
> +}
> +
> /*
> * Spawn all kthreads -- called as soon as the scheduler is running.
> */
> @@ -1783,19 +1802,24 @@ static int __init rcu_spawn_kthreads(void)
> for_each_possible_cpu(cpu) {
> init_waitqueue_head(&per_cpu(rcu_cpu_wq, cpu));
> per_cpu(rcu_cpu_has_work, cpu) = 0;
> - if (cpu_online(cpu))
> + if (cpu_online(cpu)) {
> (void)rcu_spawn_one_cpu_kthread(cpu);
> + rcu_wake_cpu_kthread(cpu);
> + }
> }
> rnp = rcu_get_root(rcu_state);
> init_waitqueue_head(&rnp->node_wq);
> rcu_init_boost_waitqueue(rnp);
> (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
> - if (NUM_RCU_NODES > 1)
> + rcu_wake_node_kthread(rnp);
> + if (NUM_RCU_NODES > 1) {
> rcu_for_each_leaf_node(rcu_state, rnp) {
> init_waitqueue_head(&rnp->node_wq);
> rcu_init_boost_waitqueue(rnp);
> (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
> + rcu_wake_node_kthread(rnp);
> }
> + }
> return 0;
> }
> early_initcall(rcu_spawn_kthreads);
> @@ -2206,7 +2230,7 @@ static void __cpuinit rcu_online_cpu(int cpu)
> rcu_preempt_init_percpu_data(cpu);
> }
>
> -static void __cpuinit rcu_online_kthreads(int cpu)
> +static void __cpuinit rcu_prepare_kthreads(int cpu)
> {
> struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
> struct rcu_node *rnp = rdp->mynode;
> @@ -2233,7 +2257,15 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
> case CPU_UP_PREPARE:
> case CPU_UP_PREPARE_FROZEN:
> rcu_online_cpu(cpu);
> - rcu_online_kthreads(cpu);
> + rcu_prepare_kthreads(cpu);
> + break;
> + case CPU_STARTING:
> + rcu_wake_cpu_kthread(cpu);
> + do {
> + struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
> + if (rdp)
> + rcu_wake_node_kthread(rdp->mynode);
> + } while (0);
> break;
> case CPU_ONLINE:
> case CPU_DOWN_FAILED:
> diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> index ed339702..961a316 100644
> --- a/kernel/rcutree_plugin.h
> +++ b/kernel/rcutree_plugin.h
> @@ -1306,7 +1306,6 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
> raw_spin_lock_irqsave(&rnp->lock, flags);
> rnp->boost_kthread_task = t;
> raw_spin_unlock_irqrestore(&rnp->lock, flags);
> - wake_up_process(t);
> sp.sched_priority = RCU_KTHREAD_PRIO;
> sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> return 0;
--
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