Subject: Re: PowerPC guest getting "BUG: scheduling while atomic" on linux-next-20210623 during secondary CPUs bringup

From: Srikar Dronamraju <[email-masked]>
Date: Fri, 25 Jun 2021 11:16:08 +0530

* Bharata B Rao <[email-masked]> [2021-06-24 21:25:09]:

> A PowerPC KVM guest gets the following BUG message when booting
> linux-next-20210623:
> 
> smp: Bringing up secondary CPUs ...
> BUG: scheduling while atomic: swapper/1/0/0x00000000
> no locks held by swapper/1/0.
> Modules linked in:
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.13.0-rc7-next-20210623
> Call Trace:
> [c00000000ae5bc20] [c000000000badc64] dump_stack_lvl+0x98/0xe0 (unreliable)
> [c00000000ae5bc60] [c000000000210200] __schedule_bug+0xb0/0xe0
> [c00000000ae5bcd0] [c000000001609e28] __schedule+0x1788/0x1c70
> [c00000000ae5be20] [c00000000160a8cc] schedule_idle+0x3c/0x70
> [c00000000ae5be50] [c00000000022984c] do_idle+0x2bc/0x420
> [c00000000ae5bf00] [c000000000229d88] cpu_startup_entry+0x38/0x40
> [c00000000ae5bf30] [c0000000000666c0] start_secondary+0x290/0x2a0
> [c00000000ae5bf90] [c00000000000be54] start_secondary_prolog+0x10/0x14
> 
> <The above repeats for all the secondary CPUs>
> 
> smp: Brought up 2 nodes, 16 CPUs
> numa: Node 0 CPUs: 0-7
> numa: Node 1 CPUs: 8-15
> 
> This seems to have started from next-20210521 and isn't seen on
> next-20210511.
> 

Bharata,

I think the regression is due to Commit f1a0a376ca0c ("sched/core:
Initialize the idle task with preemption disabled")

Can you please try with the above commit reverted?

-- 
Thanks and Regards
Srikar Dronamraju