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Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule

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On Fri, 25 Mar 2016, Mike Galbraith wrote:
> On Thu, 2016-03-24 at 12:06 +0100, Mike Galbraith wrote:
> > On Thu, 2016-03-24 at 11:44 +0100, Thomas Gleixner wrote:
> > >  
> > > > On the bright side, with the busted migrate enable business reverted,
> > > > plus one dinky change from me [1], master-rt.today has completed 100
> > > > iterations of Steven's hotplug stress script along side endless
> > > > futexstress, and is happily doing another 900 as I write this, so the
> > > > next -rt should finally be hotplug deadlock free.
> > > > 
> > > > Thomas's state machinery seems to work wonders.  'course this being
> > > > hotplug, the other shoe will likely apply itself to my backside soon.
> > > 
> > > That's a given :)
> > 
> > blk-mq applied it shortly after I was satisfied enough to poke xmit.
> 
> The other shoe is that notifiers can depend upon RCU grace periods, so
> when pin_current_cpu() snags rcu_sched, the hotplug game is over.
> 
> blk_mq_queue_reinit_notify:
>         /*
>          * We need to freeze and reinit all existing queues.  Freezing
>          * involves synchronous wait for an RCU grace period and doing it
>          * one by one may take a long time.  Start freezing all queues in
>          * one swoop and then wait for the completions so that freezing can
>          * take place in parallel.
>          */
>         list_for_each_entry(q, &all_q_list, all_q_node)
>                 blk_mq_freeze_queue_start(q);
>         list_for_each_entry(q, &all_q_list, all_q_node) {
>                 blk_mq_freeze_queue_wait(q);

Yeah, I stumbled over that already when analysing all the hotplug notifier
sites. That's definitely a horrible one.
 
> Hohum (sharpens rock), next.

/me recommends frozen sharks

Thanks,

       tglx

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Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-20 09:50 +0100
  Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-24 11:10 +0100
    Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Thomas Gleixner <tglx@linutronix.de> - 2016-03-24 11:50 +0100
      Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-24 12:10 +0100
        Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-25 06:40 +0100
          Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Thomas Gleixner <tglx@linutronix.de> - 2016-03-25 10:00 +0100
            Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-25 10:20 +0100
            Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-25 10:20 +0100
              Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-25 17:30 +0100
                Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-29 06:10 +0200
      Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-31 08:40 +0200
        Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-04-01 23:20 +0200
          Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-02 05:20 +0200

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