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

On Fri, Jun 25, 2021 at 11:16:08AM +0530, Srikar Dronamraju wrote:

* Bharata B Rao [off-list ref] [2021-06-24 21:25:09]:

quoted

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?

Yes, reverting that commit helps.

Regards,
Bharata.