[Xen-devel] Re: PROBLEM: 3.0-rc kernels unbootable since -rc3

[Julie Sullivan <kernelmail.jms@xxxxxxxxx>]

On Tue, Jul 12, 2011 at 9:46 PM, Paul E. McKenney
<paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Jul 12, 2011 at 03:57:32PM -0400, Konrad Rzeszutek Wilk wrote:
>> On Tue, Jul 12, 2011 at 09:10:36PM +0200, Peter Zijlstra wrote:
>> > On Tue, 2011-07-12 at 11:59 -0700, Paul E. McKenney wrote:
>> > > OK, so the infinite loop in task_waking_fair() happens even if RCU 
>> > > callbacks
>> > > are deferred until after the scheduler is fully initialized.  Sounds like
>> > > one for the scheduler guys.  ;-)
>> >
>> > https://lkml.org/lkml/2011/7/12/150
>>
>> Such a simple patch. And yes, it fixes the issue. You can add
>> Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> if it hasn't yet
>> showed up in Ingo's tree.
>>
>> Paul, thanks for help on this and providing ideas to test!
>
> Konrad, thank you for all the testing!
>
> Julie, if you apply Peter's patch,



But this is for 32-bit , right?

> +#ifndef CONFIG_64BIT
> +     cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
> +#endif
 }

I'm using 64-bit...

Would you still like me to try the below patch?

Cheers
Julie


> do you also need the patch shown
> below?
>
> Ravi, could you please retest with the patch below as well?
>
>                                                        Thanx, Paul
>
> ------------------------------------------------------------------------
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 7e59ffb..ba06207 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -84,9 +84,32 @@ DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
>
>  static struct rcu_state *rcu_state;
>
> +/*
> + * The rcu_scheduler_active variable transitions from zero to one just
> + * before the first task is spawned.  So when this variable is zero, RCU
> + * can assume that there is but one task, allowing RCU to (for example)
> + * optimized synchronize_sched() to a simple barrier().  When this variable
> + * is one, RCU must actually do all the hard work required to detect real
> + * grace periods.  This variable is also used to suppress boot-time false
> + * positives from lockdep-RCU error checking.
> + */
>  int rcu_scheduler_active __read_mostly;
>  EXPORT_SYMBOL_GPL(rcu_scheduler_active);
>
> +/*
> + * The rcu_scheduler_fully_active variable transitions from zero to one
> + * during the early_initcall() processing, which is after the scheduler
> + * is capable of creating new tasks.  So RCU processing (for example,
> + * creating tasks for RCU priority boosting) must be delayed until after
> + * rcu_scheduler_fully_active transitions from zero to one.  We also
> + * currently delay invocation of any RCU callbacks until after this point.
> + *
> + * It might later prove better for people registering RCU callbacks during
> + * early boot to take responsibility for these callbacks, but one step at
> + * a time.
> + */
> +static int rcu_scheduler_fully_active __read_mostly;
> +
>  #ifdef CONFIG_RCU_BOOST
>
>  /*
> @@ -98,7 +121,6 @@ DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
>  DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
>  DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
>  DEFINE_PER_CPU(char, rcu_cpu_has_work);
> -static char rcu_kthreads_spawnable;
>
>  #endif /* #ifdef CONFIG_RCU_BOOST */
>
> @@ -1467,6 +1489,8 @@ static void rcu_process_callbacks(struct softirq_action 
> *unused)
>  */
>  static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
>  {
> +       if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
> +               return;
>        if (likely(!rsp->boost)) {
>                rcu_do_batch(rsp, rdp);
>                return;
> diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> index 14dc7dd..75113cb 100644
> --- a/kernel/rcutree_plugin.h
> +++ b/kernel/rcutree_plugin.h
> @@ -1532,7 +1532,7 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
>        struct sched_param sp;
>        struct task_struct *t;
>
> -       if (!rcu_kthreads_spawnable ||
> +       if (!rcu_scheduler_fully_active ||
>            per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
>                return 0;
>        t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
> @@ -1639,7 +1639,7 @@ static int __cpuinit rcu_spawn_one_node_kthread(struct 
> rcu_state *rsp,
>        struct sched_param sp;
>        struct task_struct *t;
>
> -       if (!rcu_kthreads_spawnable ||
> +       if (!rcu_scheduler_fully_active ||
>            rnp->qsmaskinit == 0)
>                return 0;
>        if (rnp->node_kthread_task == NULL) {
> @@ -1665,7 +1665,7 @@ static int __init rcu_spawn_kthreads(void)
>        int cpu;
>        struct rcu_node *rnp;
>
> -       rcu_kthreads_spawnable = 1;
> +       rcu_scheduler_fully_active = 1;
>        for_each_possible_cpu(cpu) {
>                per_cpu(rcu_cpu_has_work, cpu) = 0;
>                if (cpu_online(cpu))
> @@ -1687,7 +1687,7 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
>        struct rcu_node *rnp = rdp->mynode;
>
>        /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
> -       if (rcu_kthreads_spawnable) {
> +       if (rcu_scheduler_fully_active) {
>                (void)rcu_spawn_one_cpu_kthread(cpu);
>                if (rnp->node_kthread_task == NULL)
>                        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
> @@ -1726,6 +1726,13 @@ static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
>  {
>  }
>
> +static int __init rcu_scheduler_really_started(void)
> +{
> +       rcu_scheduler_fully_active = 1;
> +       return 0;
> +}
> +early_initcall(rcu_scheduler_really_started);
> +
>  static void __cpuinit rcu_prepare_kthreads(int cpu)
>  {
>  }
>

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