linux-kernel - Re: [tip: sched/core] sched/core: Initialize the idle task with preemption disabled

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Date:   Wed, 07 Jul 2021 18:31:55 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Frederic Weisbecker <frederic@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Subject: Re: [tip: sched/core] sched/core: Initialize the idle task with preemption disabled

On 07/07/21 09:35, Guenter Roeck wrote:
> I think I have it. pseries_defconfig, and pseries emulation,
> started with "-smp 2" and qemu-system-ppc64:
>
> [    0.731644][    T1] smp: Bringing up secondary CPUs ...^M
> [    0.750546][    T0] BUG: scheduling while atomic: swapper/1/0/0x00000000^M
> [    0.752119][    T0] no locks held by swapper/1/0.^M
> [    0.752309][    T0] Modules linked in:^M
> [    0.752684][    T0] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.13.0-11855-g77d34a4683b0 #1^M
> [    0.753197][    T0] Call Trace:^M
> [    0.753334][    T0] [c000000008737b20] [c0000000009f9b18] .dump_stack_lvl+0xa4/0x100 (unreliable)^M
> [    0.754224][    T0] [c000000008737bb0] [c000000000190ed0] .__schedule_bug+0xa0/0xe0^M
> [    0.754459][    T0] [c000000008737c30] [c000000001182518] .__schedule+0xc08/0xd90^M
> [    0.754738][    T0] [c000000008737d20] [c000000001182b8c] .schedule_idle+0x2c/0x60^M
> [    0.754945][    T0] [c000000008737d90] [c0000000001a48ec] .do_idle+0x29c/0x3c0^M
> [    0.755145][    T0] [c000000008737e60] [c0000000001a4df0] .cpu_startup_entry+0x30/0x40^M
> [    0.755403][    T0] [c000000008737ee0] [c00000000005ef10] .start_secondary+0x2c0/0x300^M
> [    0.755621][    T0] [c000000008737f90] [c00000000000d254] start_secondary_prolog+0x10/0x14^M
> [    0.764164][    T1] smp: Brought up 1 node, 2 CPUs^M
>
> Guenter

Hmph, I was about to say I couldn't get that, but after cycling between
different PREEMPT options I finally triggered it, so thanks for that!

Same sha1 as yours, invocation is:

  qemu-system-ppc64 vmlinux -smp 2 -nographic -m 1024 -machine pseries,usb=off

with pseries_defconfig + CONFIG_DEBUG_ATOMIC_SLEEP + CONFIG_PREEMPT_VOLUNTARY

Now to dig!