Re: [PATCH] ARM:kexec:offline panic_smp_self_stop CPU

From: Russell King - ARM Linux
Date: Thu Nov 01 2018 - 07:34:43 EST


On Thu, Nov 01, 2018 at 07:20:49PM +0800, Wang Yufen wrote:
> From: Yufen Wang <wangyufen@xxxxxxxxxx>
>
> In case panic() and panic() called at the same time on different CPUS.
> For example:
> CPU 0:
> panic()
> __crash_kexec
> machine_crash_shutdown
> crash_smp_send_stop
> machine_kexec
> BUG_ON(num_online_cpus() > 1);
>
> CPU 1:
> panic()
> local_irq_disable
> panic_smp_self_stop
>
> If CPU 1 calls panic_smp_self_stop() before crash_smp_send_stop(), kdump
> fails. CPU1 can't receive the ipi irq, CPU1 will be always online.
> I changed BUG_ON to WARN in kexec crash as arm64 does, kdump also fails.
> Because num_online_cpus() > 1, can't disable the L2 in _soft_restart.
> To fix this problem, this patch split out the panic_smp_self_stop()
> and add set_cpu_online(smp_processor_id(), false).

Thanks.

I think this may as well go into arch/arm/kernel/smp.c - it won't be
required for single-CPU systems, since there aren't "other" CPUs.

It's probably also worth a comment above the function as to why we
have this.

>
> Signed-off-by: Yufen Wang <wangyufen@xxxxxxxxxx>
> ---
> arch/arm/kernel/setup.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 31940bd..151861f 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -602,6 +602,16 @@ static void __init smp_build_mpidr_hash(void)
> }
> #endif
>
> +void panic_smp_self_stop(void)
> +{
> + printk(KERN_DEBUG "CPU %u will stop doing anything useful since another CPU has paniced\n",
> + smp_processor_id());
> + set_cpu_online(smp_processor_id(), false);
> + while (1)
> + cpu_relax();
> +
> +}
> +
> static void __init setup_processor(void)
> {
> struct proc_info_list *list;
> --
> 2.7.4
>
>

--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up