linux-kernel - Re: [Fastboot] [PATCH] kexec: Fix CONFIG

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Date:	Fri, 02 Feb 2007 07:21:41 -0800
From:	Jay Lan <jlan@....com>
To:	Horms <horms@...ge.net.au>
CC:	"Zou, Nanhai" <nanhai.zou@...el.com>,
	Magnus Damm <magnus@...inux.co.jp>,
	"Luck, Tony" <tony.luck@...el.com>, linux-ia64@...r.kernel.org,
	fastboot@...ts.osdl.org, Andrew Morton <akpm@...ux-foundation.org>,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [Fastboot] [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

Horms wrote:
> On Fri, Feb 02, 2007 at 11:01:21AM +0800, Zou, Nanhai wrote:
>>>>>  void
>>>>>  machine_crash_shutdown(struct pt_regs *pt)
>>>>> @@ -132,11 +134,12 @@ kdump_cpu_freeze(struct unw_frame_info *
>>>>>       atomic_inc(&kdump_cpu_freezed);
>>>>>       kdump_status[cpuid] = 1;
>>>>>       mb();
>>>>> -     if (cpuid == 0) {
>>>>> -             for (;;)
>>>>> -                     cpu_relax();
>>>>> -     } else
>>>>> +#ifdef CONFIG_HOTPLUG_CPU
>>>>> +     if (cpuid != 0)
>>>>>               ia64_jump_to_sal(&sal_boot_rendez_state[cpuid]);
>>>>> +#endif
>>>>> +     for (;;)
>>>>> +             cpu_relax();
>>>>>  }
>>>> I trust ia64_jump_to_sal doesn't return.
>>> So do I. The main problem with the compilation seems to be that
>>> ia64_jump_to_sal() only exists if CONFIG_HOTPLUG_CPU=y.
>>> (include/asm-ia64/sal.h, arch/ia64/kernel/head.S)
>>>
>>  This may cause problem on SN platform. 
>> I remember SN requires cpu0 return to SAL rendez loop to do IRQ redirection.
>> However this needs SGI people to confirm...

SN needs slave cpus being returned to SAL rendez loop with the exception
of cpu0. It seems there is not a decent way to return cpu0, so we
decided to handle cpu0 in PROM. This above code change does not casue
problem on SN platform.

> 
> Does this mean that CONFIG_HOTPLUG_CPU may be required for kdump
> on the SN platform?

The SN platform uses the ia64_jump_to_sal() routine.

Thanks,
 - jay

-
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