Re: rcutorture: meaning of "End of test: RCU_HOTPLUG"

[Su Yue]

On 1/23/19 11:22 AM, Paul E. McKenney wrote:
> On Tue, Jan 22, 2019 at 04:42:19PM +0800, Su Yue wrote:
> > Thanks for your quick reply! Paul
> >
> > On 1/22/19 12:01 PM, Paul E. McKenney wrote:
> > > On Tue, Jan 22, 2019 at 11:40:53AM +0800, Su Yue wrote:
> > > > Hi, guys
> > > >    While running rcutorture tests with "onoff_interval", some tests
> > > > failed and results show like:
> > > >
> > > > =====================================================================
> > > > [  316.354501] srcud-torture:--- End of test: RCU_HOTPLUG:
> > > > nreaders=1 nfakewriters=4 stat_interval=60 verbose=2
> > > > test_no_idle_hz=1 shuffle_interval=3 stutter=5 irqreader=1 fq\
> > > > s_duration=0 fqs_holdoff=0 fqs_stutter=3 test_boost=1/0
> > > > test_boost_interval=7 test_boost_duration=4 shutdown_secs=0
> > > > stall_cpu=0 stall_cpu_holdoff=10 stall_cpu_irqsoff=0 n_ba\
> > > > rrier_cbs=0 onoff_interval=3 onoff_holdoff=0
> > > > ====================================================================
> > > >
> > > > I am wondering that meaning of "RCU_HOTPLUG". Is it expected because
> > > > cpu hotplug is enabled in the test? Or just represents another type of
> > > > failure?
> > >
> > > This says that at least one CPU hotplug operation failed, that is,
> > > the CPU didn't actually come online or go offline as requested.  If you
> > > are introducing CPU hotplug to an architecture, this usually indicates
> > > that you have bugs in your CPU-hotplug code.  Or it nmight be that
> >
> > It should hit the case since there is no RCU CPU stall warnings.
> >
> > > RCU grace periods failed to progress -- though this would normally
> > > also result in RCU CPU stall warnings.
> > >
> > > There should be lines containing "ver:" in your console output.  What
> > > does one of the later one of these say?
> >
> > The line says:
> > ======================================================================
> > [  318.850175] busted_srcud-torture: rtc:           (null) ver:
> > 27040 tfle: 0 rta: 27040 rtaf: 0 rtf: 27027 rtmbe: 0 rtbe: 0 rtbke:
> > 0 rtbre: 0 rtbf: 0 rtb: 0 \
> > nt: 9497 onoff: 2639/2639:2640/5310 40,373:10,355 162868:67542
> > (HZ=1000) barrier: 0/0:0
>
> Yes, you have many more offline attempts than successes, which is
> why RCU_HOTPLUG was printed.
>
> > =====================================================================
> >
> > And here are useful errors:
> > =====================================================================
> > kern  :info  : [  135.379693] KVM setup async PF for cpu 1
> > kern  :info  : [  135.381412] kvm-stealtime: cpu 1, msr 23fd16180
> > kern  :alert : [  135.386897] busted_srcud-torture:torture_onoff
>
> Just so your know, busted_srcud can sometimes fail by design.  Hence
> the "busted" in the name.  But failure didn't happen this time.

Yes..The corner case I mentioned actually happened in every "onoff"
tests whatever the torture_type is.

> > task: onlined 1
> > kern  :alert : [  135.408241] busted_srcud-torture:torture_onoff
> > task: offlining 1
> > kern  :info  : [  135.423310] Unregister pv shared memory for cpu 1
> > kern  :info  : [  135.427940] smpboot: CPU 1 is now offline
> > kern  :alert : [  135.430106] busted_srcud-torture:torture_onoff
> > task: offlined 1
> > kern  :alert : [  135.436404] busted_srcud-torture:torture_onoff
> > task: offlining 0
> > kern  :alert : [  135.446173] busted_srcud-torture:torture_onoff
> > task: offline 0 failed: errno -16
> > kern  :alert : [  135.453076] busted_srcud-torture:torture_onoff
> > task: offlining 0
> > kern  :alert : [  135.457461] busted_srcud-torture:torture_onoff
> > task: offline 0 failed: errno -16
> >
> >
> > =====================================================================
> > There are only two CPUs on the VM. Torture try to offline the last one
> > but -EBUSY occured.
> >
> > I spent time to understand kernel/torture.c.
> > There is torture_onoff():
> >
> > 225        while (!torture_must_stop()) {
> > 226                cpu = (torture_random(&rand) >> 4) % (maxcpu + 1);
> > 227                if (!torture_offline(cpu,
> > 228                                     &n_offline_attempts,
> > &n_offline_successes,
> > 229                                     &sum_offline, &min_offline,
> > &max_offline))
> > 230                        torture_online(cpu,
> > 231                                       &n_online_attempts,
> > &n_online_successes,
> > 232                                       &sum_online, &min_online,
> > &max_online);
> > 233                schedule_timeout_interruptible(onoff_interval);
> > 234        }
> > 235
> >
> > torture_offline() and torture_offline() don't pre judge if the current
> > cpu is only one usable.
>
> That does appear to be the case, and that would be a problem with
> the CONFIG_BOOTPARAM_HOTPLUG_CPU0 listed below.
>
> Good catch!
>
> > Our test machines are configured with CONFIG_BOOTPARAM_HOTPLUG_CPU0. If
> > there are only one oneline and hotplugable cpux, then
> > n_offline_successes != n_offline_attempts which caused "End of test:
> > RCU_HOTPLUG".
> >
> > Does I misunderstand something above? Feel free to correct me.
>
> Does the following patch help?

Yes, no more "errnor: -16" in dmesg and "End of test: SUCCESS" is in
the end.

Thanks for your patch.
If the patch is to be sent in format, you can add:

Tested-By: Su Yue <suy.fnst@xxxxxxxxxxxxxx>


---
Su
> 							Thanx, Paul
>
> ------------------------------------------------------------------------
>
> diff --git a/kernel/torture.c b/kernel/torture.c
> index a03ff722352b..2b6700ca2a43 100644
> --- a/kernel/torture.c
> +++ b/kernel/torture.c
> @@ -101,6 +101,8 @@ bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
>   
>   	if (!cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
>   		return false;
> +	if (num_online_cpus() <= 1)
> +		return false;  /* Can't offline the last CPU. */
>   
>   	if (verbose > 1)
>   		pr_alert("%s" TORTURE_FLAG