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Date: Tue, 03 Mar 2015 15:13:07 -0500 From: Boris Ostrovsky <boris.ostrovsky@...cle.com> To: paulmck@...ux.vnet.ibm.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 03/03/2015 02:42 PM, Paul E. McKenney wrote: > 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); > } else pr_err("CPU %u didn't die...\n", 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? I believe PV VCPUs will always be CPU_DEAD by the time we get here since we are (indirectly) waiting for this in the loop at the beginning of xen_cpu_die(): 'while (xen_pv_domain() && HYPERVISOR_vcpu_op(VCPUOP_is_up, cpu, NULL))' will exit only after 'HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id()' in xen_play_dead(). Which happens after play_dead_common() has marked the cpu as CPU_DEAD. So no test is needed. Thanks. -boris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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