linux-kernel - Re: localed stuck in recent 3.18 git in copy_net

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Message-ID: <10136.1414196448@famine>
Date:	Fri, 24 Oct 2014 17:20:48 -0700
From:	Jay Vosburgh <jay.vosburgh@...onical.com>
To:	paulmck@...ux.vnet.ibm.com
cc:	Yanko Kaneti <yaneti@...lera.com>,
	Josh Boyer <jwboyer@...oraproject.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Cong Wang <cwang@...pensource.com>,
	Kevin Fenzi <kevin@...ye.com>, netdev <netdev@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	mroos@...ux.ee, tj@...nel.org
Subject: Re: localed stuck in recent 3.18 git in copy_net_ns?

Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

>On Fri, Oct 24, 2014 at 03:59:31PM -0700, Paul E. McKenney wrote:
[...]
>> Hmmm...  It sure looks like we have some callbacks stuck here.  I clearly
>> need to take a hard look at the sleep/wakeup code.
>> 
>> Thank you for running this!!!
>
>Could you please try the following patch?  If no joy, could you please
>add rcu:rcu_nocb_wake to the list of ftrace events?

	I tried the patch, it did not change the behavior.

	I enabled the rcu:rcu_barrier and rcu:rcu_nocb_wake tracepoints
and ran it again (with this patch and the first patch from earlier
today); the trace output is a bit on the large side so I put it and the
dmesg log at:

http://people.canonical.com/~jvosburgh/nocb-wake-dmesg.txt

http://people.canonical.com/~jvosburgh/nocb-wake-trace.txt

	-J


>							Thanx, Paul
>
>------------------------------------------------------------------------
>
>rcu: Kick rcuo kthreads after their CPU goes offline
>
>If a no-CBs CPU were to post an RCU callback with interrupts disabled
>after it entered the idle loop for the last time, there might be no
>deferred wakeup for the corresponding rcuo kthreads.  This commit
>therefore adds a set of calls to do_nocb_deferred_wakeup() after the
>CPU has gone completely offline.
>
>Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>
>diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>index 84b41b3c6ebd..f6880052b917 100644
>--- a/kernel/rcu/tree.c
>+++ b/kernel/rcu/tree.c
>@@ -3493,8 +3493,10 @@ static int rcu_cpu_notify(struct notifier_block *self,
> 	case CPU_DEAD_FROZEN:
> 	case CPU_UP_CANCELED:
> 	case CPU_UP_CANCELED_FROZEN:
>-		for_each_rcu_flavor(rsp)
>+		for_each_rcu_flavor(rsp) {
> 			rcu_cleanup_dead_cpu(cpu, rsp);
>+			do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
>+		}
> 		break;
> 	default:
> 		break;
>

---
	-Jay Vosburgh, jay.vosburgh@...onical.com
--
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