Re: sched/core warning triggers on rcu torture test

[Frederic Weisbecker]

On Tue, Jun 26, 2018 at 06:16:04PM +0200, Anna-Maria Gleixner wrote:
> Hi,
> 
> during rcu torture tests (TREE04 and TREE07) I noticed, that a
> WARN_ON_ONCE() in sched core triggers on a recent 4.18-rc2 based
> kernel (6f0d349d922b ("Merge
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net")) as well as
> on a 4.17.3.
> 
> I'm running the tests on a machine with 144 cores:
> 
>   tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 144 --duration 120 --configs "9*TREE07"
>   tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 144 --duration 120 --configs "18*TREE04"
> 
> 
> The warning was introduced by commit d84b31313ef8 ("sched/isolation:
> Offload residual 1Hz scheduler tick").
> 
> 
> Output looks similar for all tests I did (this one is the output of
> the 4.18-rc2 based kernel):
> 
> WARNING: CPU: 11 PID: 906 at kernel/sched/core.c:3138 sched_tick_remote+0xb6/0xc0
> Modules linked in:
> CPU: 11 PID: 906 Comm: kworker/u32:3 Not tainted 4.18.0-rc2+ #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> Workqueue: events_unbound sched_tick_remote
> RIP: 0010:sched_tick_remote+0xb6/0xc0
> Code: e8 0f 06 b8 00 c6 03 00 fb eb 9d 8b 43 04 85 c0 75 8d 48 8b 83 e0 0a 00 00 48 85 c0 75 81 eb 88 48 89 df e8 bc fe ff ff eb aa <0f> 0b eb c5 66 0f 1f 44 00 00 bf 17 00 00 00 e8 b6 2e fe ff 0f b6
> Call Trace:
>  process_one_work+0x1df/0x3b0
>  worker_thread+0x44/0x3d0
>  kthread+0xf3/0x130
>  ? set_worker_desc+0xb0/0xb0
>  ? kthread_create_worker_on_cpu+0x70/0x70
>  ret_from_fork+0x35/0x40
> ---[ end trace 7c99b83eb0ec64e8 ]---
> 
> 
> Do you need some more information?
> 
> 
> Thanks,
> 
> 	Anna-Maria


Ok so now I reproduce it immediately after the boot, time for me to debug :-)

Thanks.