Re: [PATCH] ARM: kexec: offline non panic CPUs on Kdump panic

Will Deacon
2013-07-26T10:49:08Z

[Adding Stephen Warren since he has been working in this area]

On Fri, Jul 26, 2013 at 06:41:27AM +0100, vijay.kilari@gmail.com wrote:
> From: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
>
> In case of normal kexec kernel load, all cpu's are offlined
> before calling machine_kexec() under kernel_kexec() function.
> But in case crash panic cpus are relaxed in
> machine_crash_nonpanic_core() SMP function but not offlined.
>
> When crash kernel is loaded with kexec and on panic trigger
> machine_kexec() checks for number of cpus online.
> If more than one cpu is online machine_kexec() fails to load
> with below error
>
> kexec: error: multiple CPUs still online
>
> In machine_crash_nonpanic_core() SMP function, offline CPU
> before cpu_relax
>
> Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
> ---
> arch/arm/kernel/machine_kexec.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
> index 4fb074c..163b160 100644
> --- a/arch/arm/kernel/machine_kexec.c
> +++ b/arch/arm/kernel/machine_kexec.c
> @@ -73,6 +73,7 @@ void machine_crash_nonpanic_core(void *unused)
> crash_save_cpu(&regs, smp_processor_id());
> flush_cache_all();
>
> + set_cpu_online(smp_processor_id(), false);
> atomic_dec(&waiting_for_crash_ipi);
> while (1)
> cpu_relax();

Ok, I guess this will work since the new kernel is loaded somewhere higher
in memory and the crashed kernel will stick around, so the non-crashing CPUs
can sit around spinning.

Will