Re: NMI Reported with

From: John Ogness
Date: Fri Feb 09 2024 - 04:12:20 EST

Hi John,

On 2024-02-07, "John B. Wyatt IV" <jwyatt@xxxxxxxxxx> wrote:
> You asked me to test the upstream kernel with a printk torture
> ( with the different scheduler settings on a very
> large core system. Wanted to post to the mailing list to show what I
> tested with.

Thanks for your efforts here!

> As far as I can tell; all the scheduler settings correctly get to and
> trip the sysrq trigger to make it crash at the end of the script.
> But, with every state, except for fully pre-emeptive, I got an NMI
> call trace before the sysrq trigger that expectedly crashes the
> system.
> This is on a Fedora 39 Server installed on a 2x56 core, 224 thread
> machine in Red Hat's lab with the lscpu below with 6.7.0-rt6. I have
> only decoded and attached NoForcedPreemption below. Please ask if you
> want additional ones but they all look similar when I checked.
> NMI Call Trace for NoForcedPreemption
> ---
> task:cpuhp/222 state:S stack:0 pid:1349 tgid:1349 ppid:2 flags:0x00004000
> Call Trace:
> <TASK>
> __schedule (kernel/sched/core.c:5396 kernel/sched/core.c:6708)
> ? try_to_wake_up (./arch/x86/include/asm/preempt.h:104 ./include/linux/preempt.h:484 ./include/linux/preempt.h:484 kernel/sched/core.c:4217)
> ? __pfx_smpboot_thread_fn (kernel/smpboot.c:107)
> schedule (kernel/sched/core.c:6784 kernel/sched/core.c:6798)
> smpboot_thread_fn (kernel/smpboot.c:160)
> kthread (kernel/kthread.c:388)
> ? __pfx_kthread (kernel/kthread.c:341)
> ret_from_fork (arch/x86/kernel/process.c:147)
> ? __pfx_kthread (kernel/kthread.c:341)
> ret_from_fork_asm (arch/x86/entry/entry_64.S:250)
> </TASK>
> sysrq: Trigger a crash
> Kernel panic - not syncing: sysrq triggered crash
> NMI backtrace for cpu 56
> Hardware name: Intel Corporation D50DNP1SBB/D50DNP1SBB, BIOS SE5C7411.86B.9409.D04.2212261349 12/26/2022
> RIP: 0010:io_serial_in (arch/x86/kernel/early_printk.c:100)

I am curious why early_printk is here. Are you using KDB or KGDB?

Could you provide me your kernel config and boot args?

On a side note, it is helpful to use a kernel that prints timing and
caller information:


Timing information can also be turned on dynamically with the boot arg
"printk.time=1" but the caller information (which is more interesting)
can only be enabled in the kernel build.

John Ogness