Re: [PATCH for stable 5.x] rcu: Tighten rcu_advance_cbs_nowake() checks

[Guillaume Morin <guillaume@morinfr.org>]

On 20 Jan 12:57, Paul E. McKenney wrote:
>
> On Thu, Jan 20, 2022 at 08:26:54PM +0100, Guillaume Morin wrote:
> > On 20 Jan 11:16, Paul E. McKenney wrote:
> > > On Thu, Jan 20, 2022 at 07:55:01PM +0100, Guillaume Morin wrote:
> > > > I believe commit 614ddad17f22a22e035e2ea37a04815f50362017 (slated for
> > > > 5.17) should be queued for all 5.4+ stable branches as it fixes a
> > > > serious lockup bug. FWIW I have verified it applies cleanly on all 4
> > > > branches.
> > > > 
> > > > Does that make sense to you?
> > > 
> > > From a quick glance at v5.4, it looks quite plausible to me.
> > > 
> > > I do suggest that you try building and testing, given that the hardware's
> > > idea of what is plausible overrides that of either of us.  ;-)
> > 
> > We've had a few dozens lockups on 5.4 and 5.10 due to this bug (what
> > lead me to write to you back in Sep). The original bugzilla report is on
> > 5.4 as well, see https://bugzilla.kernel.org/show_bug.cgi?id=208685. So
> > I am positive that the issue is reachable in both kernels.
> > 
> > Also I do know for sure it fixes the problem for 5.10. I don't have a
> > test rig anymore for 5.4. But considering we know it's reachable with
> > 5.4, I think the patch should be applied for 5.4+. Obviously, you're the
> > expert here though.
> 
> Au contraire!  I do not claim much expertise on -stable validation.
> 
> If it was me, I would run a quick touch-test like this from the top-level
> directory of the Linux-kernel source tree on a qemu/KVM-capable system:
> 
> 	tools/testing/selftests/rcutorture/bin/kvm.sh --cpus N --duration 10 --configs "TREE01 TREE04"
> 
> Where "N" is replaced by the number of CPUs on your system, which should
> preferably be at least eight.
> 
> This will take somewhere between 15 minutes and an hour to run, depending
> on your system.
> 
> Sadly, v5.4 isn't quite as good at analyzing results as are current
> versions, but please feel free to send me the output.
> 
> Does that help?

Ok I did a quick run with 614ddad17f22a22e035e2ea37a04815f50362017
applied on top of the 5.4 stable branch. Not quite sure how I got
suckered into running a test on a kernel I don't even run, but hey I
guess everybody must do their part :-)

Not sure about CONFIG_HOTPLUG_CPU thing at the end.

tools/testing/selftests/rcutorture/initrd/init already exists, no need to create it
Results directory: /usr/scratch/kernel/tools/testing/selftests/rcutorture/res/2022.01.20-17:02:37
tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 60 --duration 10 --configs TREE01 TREE04
----Start batch 1: Thu 20 Jan 2022 05:02:37 PM EST
TREE01 8: Starting build. Thu 20 Jan 2022 05:02:37 PM EST
TREE01 8: Waiting for build to complete. Thu 20 Jan 2022 05:02:37 PM EST
TREE01 8: Build complete. Thu 20 Jan 2022 05:03:16 PM EST
TREE04 8: Starting build. Thu 20 Jan 2022 05:03:16 PM EST
TREE04 8: Waiting for build to complete. Thu 20 Jan 2022 05:03:16 PM EST
TREE04 8: Build complete. Thu 20 Jan 2022 05:03:55 PM EST
---- TREE01 8: Kernel present. Thu 20 Jan 2022 05:03:55 PM EST
---- TREE04 8: Kernel present. Thu 20 Jan 2022 05:03:55 PM EST
---- Starting kernels. Thu 20 Jan 2022 05:03:55 PM EST
---- All kernel runs complete. Thu 20 Jan 2022 05:14:05 PM EST
---- TREE01 8: Build/run results:
 --- Thu 20 Jan 2022 05:02:37 PM EST: Starting build
 --- Thu 20 Jan 2022 05:03:55 PM EST: Starting kernel
CPU-hotplug kernel, adding rcutorture onoff.
Monitoring qemu job at pid 46081
Grace period for qemu job at pid 46081
---- TREE04 8: Build/run results:
 --- Thu 20 Jan 2022 05:03:16 PM EST: Starting build
:CONFIG_HOTPLUG_CPU: improperly set
 --- Thu 20 Jan 2022 05:03:55 PM EST: Starting kernel
CPU-hotplug kernel, adding rcutorture onoff.
Monitoring qemu job at pid 45847
Grace period for qemu job at pid 45847


 --- Thu 20 Jan 2022 05:02:37 PM EST Test summary:
Results directory: /usr/scratch/kernel/tools/testing/selftests/rcutorture/res/2022.01.20-17:02:37
tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 60 --duration 10 --configs TREE01 TREE04
TREE01 ------- 12719 GPs (21.1983/s) [rcu: g94609 f0x0 ]
TREE04 ------- 3128 GPs (5.21333/s) [rcu: g23621 f0x0 ]
:CONFIG_HOTPLUG_CPU: improperly set


-- 
Guillaume Morin <guillaume@morinfr.org>