Re: [BUG REPORT] Triggering a panic in an x86 virtual machine does not wait

[Baokun Li <libaokun1@huawei.com>]

On 2023/7/5 16:59, Thomas Gleixner wrote:
> On Mon, Jul 03 2023 at 11:44, Baokun Li wrote:
>
>> When I manually trigger panic in a qume x86 VM with
>>
>>          `echo c > /proc/sysrq-trigger`,
>>
>>    I find that the VM will probably reboot directly, but the
>> PANIC_TIMEOUT is 0.
>> This prevents us from exporting the vmcore via panic, and even if we succeed
>> in panic exporting the vmcore, the processes in the vmcore are mostly
>> stop_this_cpu(). By dichotomizing we found the patch that introduced the
>> behavior change
>>
>>      45e34c8af58f ("x86/smp: Put CPUs into INIT on shutdown if possible"),
> Bah, I missed that this is used by crash too. So if this happens to be
> invoked on an AP, i.e. not on CPU 0, then the INIT will reset the
> machine. Fix below.
>
> Thanks,
>
>          tglx
> ---
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index ed2d51960a7d..e1aa2cd7734b 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1348,6 +1348,14 @@ bool smp_park_other_cpus_in_init(void)
>   	if (apic->wakeup_secondary_cpu_64 || apic->wakeup_secondary_cpu)
>   		return false;
>   
> +	/*
> +	 * If this is a crash stop which does not execute on the boot CPU,
> +	 * then this cannot use the INIT mechanism because INIT to the boot
> +	 * CPU will reset the machine.
> +	 */
> +	if (this_cpu)
> +		return false;
> +
>   	for_each_present_cpu(cpu) {
>   		if (cpu == this_cpu)
>   			continue;
This patch does fix the problem of rebooting at panic, but the exported 
stack
stays at stop_this_cpu() like below, instead of showing what the 
corresponding
process is doing as before.

PID: 681      TASK: ffff9ac2429d3080  CPU: 2    COMMAND: "fsstress"
  #0 [ffffb00200184fd0] stop_this_cpu at ffffffff89a4ffd8
  #1 [ffffb00200184fe8] __sysvec_reboot at ffffffff89a94213
  #2 [ffffb00200184ff0] sysvec_reboot at ffffffff8aee7491
--- <IRQ stack> ---
     RIP: 0000000000000010  RSP: 0000000000000018  RFLAGS: ffffb00200f8bd08
     RAX: ffff9ac256fda9d8  RBX: 0000000009973a85  RCX: ffff9ac256fda078
     RDX: ffff9ac24416e300  RSI: ffff9ac256fda9e0  RDI: ffffffffffffffff
     RBP: ffff9ac2443a5f88   R8: 0000000000000000   R9: ffff9ac2422eeea0
     R10: ffff9ac256fda9d8  R11: 0000000000549921  R12: ffff9ac2422eeea0
     R13: ffff9ac251cd23c8  R14: ffff9ac24269a800  R15: ffff9ac251cd2150
     ORIG_RAX: ffffffff8a1719e4  CS: 0206  SS: ffffffff8a1719c8
bt: WARNING: possibly bogus exception frame

Do you know how this happened? I would be grateful if you could fix it.

Thanks!
-- 
With Best Regards,
Baokun Li
.