ARM kexec SMP problem using exynos4210

Hi,

I have tested kexec to Nuri board using Exynos4210(Dual-core ARM Cortex-A9) on the latest mainline kernel but i am facing one problem.

The kernel enabled SMP, kernel_kexec() calls machine_shutdown to stop all cpus except current cpu and jumps to the new kernel but the kernel is hanged soon.

I used cpu_down(1) to make disabled cpu1 instead of smp_send_stop of machine_shutdown and it is booted successfully to new kernel.

Any ideas?

Quoted 1 line · Joonyoung Shim

Hi,

Hello [adding linux-arm-kernel],

Quoted 11 lines

I have tested kexec to Nuri board using Exynos4210(Dual-core ARM Cortex-A9) on the latest mainline kernel but i am facing one problem.

The kernel enabled SMP, kernel_kexec() calls machine_shutdown to stop all cpus except current cpu and jumps to the new kernel but the kernel is hanged soon.

I used cpu_down(1) to make disabled cpu1 instead of smp_send_stop of machine_shutdown and it is booted successfully to new kernel.

Any ideas?

I suspect that the secondary CPUs are not being parked correctly in the first kernel. For this, you need to implement platform_cpu_kill for your platform.

Given that exynos just does:

int platform_cpu_kill(unsigned int cpu)

{
	return 1;
}

then I'm not surprised it doesn't work. Try adding something in there which puts the CPU into a state where it can be booted by the next kernel.

I considered adding a purely software mechanism for doing this (in fact, I prototyped something up on vexpress) but after discussions with some board maintainers it became clear that most SMP SoCs have hardware assists for hotplug, and the software approach is really only need for things like the ARM development boards.

Will

One more question, generally boot cpu is first cpu(cpu0). If current cpu is secondary cpu(cpu1), smp_send_stop of machine_shutdown will stop first cpu and next kernel will try to boot on secondary cpu. Is it possible?

Quoted 4 lines · Joonyoung Shim

One more question, generally boot cpu is first cpu(cpu0). If current cpu is secondary cpu(cpu1), smp_send_stop of machine_shutdown will stop first cpu and next kernel will try to boot on secondary cpu. Is it possible?

I added the cpu_logical_map stuff for this, so the kernel can handle it. That said, your platform may have restrictions about the boot CPU so if it doesn't work, you'll need to taskset the kexec command to CPU 0.

Quoted 6 lines · Will Deacon

Quoted 4 lines · Joonyoung Shim

One more question, generally boot cpu is first cpu(cpu0). If current cpu is secondary cpu(cpu1), smp_send_stop of machine_shutdown will stop first cpu and next kernel will try to boot on secondary cpu. Is it possible?

Quoted 3 lines

I added the cpu_logical_map stuff for this, so the kernel can handle it. That said, your platform may have restrictions about the boot CPU so if it doesn't work, you'll need to taskset the kexec command to CPU 0.

Would this negatively effect kdump though where you might not be able to switch back to cpu0? I think It's best to be able to boot on any core.