linux-kernel - Re: [PATCH tip/core/rcu 02/20] x86: Use common outgoing-CPU-notification code

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Date:	Tue, 3 Mar 2015 11:42:23 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com, x86@...nel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH tip/core/rcu 02/20] x86: Use common
 outgoing-CPU-notification code

On Tue, Mar 03, 2015 at 02:17:24PM -0500, Boris Ostrovsky wrote:
> On 03/03/2015 12:42 PM, Paul E. McKenney wrote:
> >  }
> >@@ -511,7 +508,8 @@ static void xen_cpu_die(unsigned int cpu)
> >  		schedule_timeout(HZ/10);
> >  	}
> >-	cpu_die_common(cpu);
> >+	(void)cpu_wait_death(cpu, 5);
> >+	/* FIXME: Are the below calls really safe in case of timeout? */
> 
> 
> Not for HVM guests (PV guests will only reach this point after
> target cpu has been marked as down by the hypervisor).
> 
> We need at least to have a message similar to what native_cpu_die()
> prints on cpu_wait_death() failure. And I think we should not call
> the two routines below (three, actually --- there is also
> xen_teardown_timer() below, which is not part of the diff).
> 
> -boris
> 
> 
> >  	xen_smp_intr_free(cpu);
> >  	xen_uninit_lock_cpu(cpu);

So something like this, then?

	if (cpu_wait_death(cpu, 5)) {
		xen_smp_intr_free(cpu);
		xen_uninit_lock_cpu(cpu);
		xen_teardown_timer(cpu);
	}

Easy change for me to make if so!

Or do I need some other check for HVM-vs.-PV guests, and, if so, what
would that check be?  And also if so, is it OK to online a PV guest's
CPU that timed out during its previous offline?

							Thanx, Paul

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