[PATCH] x86: make reboot task only run on the appropriate processor

[WANG Chao]

On 11/08/13 at 10:14am, Vivek Goyal wrote:
> On Tue, Nov 05, 2013 at 05:16:07PM +0800, Baoquan He wrote:
> > Currently system always reboot after below message when execute "kexec -e".
> > 
> > [    0.572119] smpboot: Booting Node   0, Processors  #   1 OK
> > 
> > In commit 1b3a5d02ee070c8f9943333b9b6370f486601e0f, reboot= handling was
> > moved to kerne/reboot.c. However, the code to migrate current thread to
> > reboot cpu was removed. That cause this incorrect kexec behavior.
> > 
> > Now add that code block back.
> > 
> > Reported-by: Matthew Whitehead <mwhitehe at redhat.com>
> > Reported-by: Dave Young <dyoung at redhat.com>
> > Tested-by: WANG Chao <chaowang at redhat.com>
> > Signed-off-by: Baoquan He <bhe at redhat.com>
> 
> Hi Bao,
> 
> This patch fixes the issue for me too. I noticed that we have generic
> function migrate_to_reboot_cpu() to achieve what we want and rest of
> the reboot paths are using it. So how about using that function. I 
> wrote the new patch below. It works for me. Can you please give it
> a try.

Hi, Vivek

I confirm this patch works for me, even in a nested kexec scenario. Feel
free to add these:

Bisected-by: WANG Chao <chaowang at redhat.com>
Tested-by: WANG Chao <chaowang at redhat.com>

Thanks
WANG Chao

> 
> Thanks
> Vivek
> 
> kexec: migrate to reboot cpu
> 
> Commit 1b3a5d02ee070c8f9943333b9b6370f486601e0f moved reboot= handling to
> generic code. In the process it also removed the code in
> native_machine_shutdown() which are moving reboot process to reboot_cpu/cpu0.
> 
> I guess that thought must have been that all reboot paths are calling
> migrate_to_reboot_cpu(), so we don't need this special handling. But
> kexec reboot path (kernel_kexec()) is not calling migrate_to_reboot_cpu()
> so above change broke kexec. Now reboot can happen on non-boot cpu and when
> INIT is sent in second kerneo to bring up BP, it brings down the machine.
> 
> So start calling migrate_to_reboot_cpu() in kexec reboot path to avoid
> this problem.
> 
> Reported-by: Matthew Whitehead <mwhitehe at redhat.com>
> Reported-by: Dave Young <dyoung at redhat.com>
> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> ---
>  include/linux/reboot.h |    1 +
>  kernel/kexec.c         |    1 +
>  kernel/reboot.c        |    2 +-
>  3 files changed, 3 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/kernel/reboot.c
> ===================================================================
> --- linux-2.6.orig/kernel/reboot.c	2013-10-16 00:30:50.000000000 -0400
> +++ linux-2.6/kernel/reboot.c	2013-11-08 21:31:03.379064848 -0500
> @@ -104,7 +104,7 @@ int unregister_reboot_notifier(struct no
>  }
>  EXPORT_SYMBOL(unregister_reboot_notifier);
>  
> -static void migrate_to_reboot_cpu(void)
> +void migrate_to_reboot_cpu(void)
>  {
>  	/* The boot cpu is always logical cpu 0 */
>  	int cpu = reboot_cpu;
> Index: linux-2.6/include/linux/reboot.h
> ===================================================================
> --- linux-2.6.orig/include/linux/reboot.h	2013-11-08 21:33:27.000000000 -0500
> +++ linux-2.6/include/linux/reboot.h	2013-11-08 21:34:29.778073522 -0500
> @@ -43,6 +43,7 @@ extern int unregister_reboot_notifier(st
>   * Architecture-specific implementations of sys_reboot commands.
>   */
>  
> +extern void migrate_to_reboot_cpu(void);
>  extern void machine_restart(char *cmd);
>  extern void machine_halt(void);
>  extern void machine_power_off(void);
> Index: linux-2.6/kernel/kexec.c
> ===================================================================
> --- linux-2.6.orig/kernel/kexec.c	2013-10-16 00:30:50.000000000 -0400
> +++ linux-2.6/kernel/kexec.c	2013-11-08 21:34:02.492072375 -0500
> @@ -1676,6 +1676,7 @@ int kernel_kexec(void)
>  #endif
>  	{
>  		kernel_restart_prepare(NULL);
> +		migrate_to_reboot_cpu();
>  		printk(KERN_EMERG "Starting new kernel\n");
>  		machine_shutdown();
>  	}