[PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Magnus Damm]

kexec: Fix CONFIG_SMP=n compilation (ia64)

This patch makes it possible to compile kexec for ia64 without SMP support.

Signed-off-by: Magnus Damm <magnus@valinux.co.jp>
---

 Applies on top of 2.6.20-rc7.

 arch/ia64/kernel/crash.c         |   11 +++++++----
 arch/ia64/kernel/machine_kexec.c |    2 ++
 2 files changed, 9 insertions(+), 4 deletions(-)

--- 0002/arch/ia64/kernel/crash.c
+++ work/arch/ia64/kernel/crash.c	2007-02-01 12:42:38.000000000 +0900
@@ -79,6 +79,7 @@ crash_save_this_cpu()
 	final_note(buf);
 }
 
+#ifdef CONFIG_SMP
 static int
 kdump_wait_cpu_freeze(void)
 {
@@ -91,6 +92,7 @@ kdump_wait_cpu_freeze(void)
 	}
 	return 1;
 }
+#endif
 
 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();
 }
 
 static int
--- 0002/arch/ia64/kernel/machine_kexec.c
+++ work/arch/ia64/kernel/machine_kexec.c	2007-02-01 12:35:46.000000000 +0900
@@ -70,12 +70,14 @@ void machine_kexec_cleanup(struct kimage
 
 void machine_shutdown(void)
 {
+#ifdef CONFIG_SMP
 	int cpu;
 
 	for_each_online_cpu(cpu) {
 		if (cpu != smp_processor_id())
 			cpu_down(cpu);
 	}
+#endif
 	kexec_disable_iosapic();
 }

Re: [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Andrew Morton]

(added ia64 list)
(added ia64 maintainer)
(added kexec list)

On Thu, 01 Feb 2007 22:13:47 +0900
Magnus Damm <magnus@valinux.co.jp> wrote:

> kexec: Fix CONFIG_SMP=n compilation (ia64)
> 
> This patch makes it possible to compile kexec for ia64 without SMP support.
> 

Please always include the compiler stderr when fixing build errors or
warnings.

> 
>  Applies on top of 2.6.20-rc7.
> 
>  arch/ia64/kernel/crash.c         |   11 +++++++----
>  arch/ia64/kernel/machine_kexec.c |    2 ++
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> --- 0002/arch/ia64/kernel/crash.c
> +++ work/arch/ia64/kernel/crash.c	2007-02-01 12:42:38.000000000 +0900
> @@ -79,6 +79,7 @@ crash_save_this_cpu()
>  	final_note(buf);
>  }
>  
> +#ifdef CONFIG_SMP
>  static int
>  kdump_wait_cpu_freeze(void)
>  {
> @@ -91,6 +92,7 @@ kdump_wait_cpu_freeze(void)
>  	}
>  	return 1;
>  }
> +#endif

I think this is a warning fix?

>  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.

>  static int
> --- 0002/arch/ia64/kernel/machine_kexec.c
> +++ work/arch/ia64/kernel/machine_kexec.c	2007-02-01 12:35:46.000000000 +0900
> @@ -70,12 +70,14 @@ void machine_kexec_cleanup(struct kimage
>  
>  void machine_shutdown(void)
>  {
> +#ifdef CONFIG_SMP
>  	int cpu;
>  
>  	for_each_online_cpu(cpu) {
>  		if (cpu != smp_processor_id())
>  			cpu_down(cpu);
>  	}
> +#endif
>  	kexec_disable_iosapic();
>  }

hm.  I suspect this one should have been #ifndef CONFIG_HOTPLUG_CPU?

I was wondering if we should have stubs for cpu_down() if !CONFIG_HOTPLUG_CPU,
but perhaps that doesn't make sense.

Re: [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Magnus Damm]

On 2/2/07, Andrew Morton <akpm@linux-foundation.org> wrote:
>
> (added ia64 list)
> (added ia64 maintainer)
> (added kexec list)

Sorry about that.

> On Thu, 01 Feb 2007 22:13:47 +0900
> Magnus Damm <magnus@valinux.co.jp> wrote:
>
> > kexec: Fix CONFIG_SMP=n compilation (ia64)
> >
> > This patch makes it possible to compile kexec for ia64 without SMP support.
> >
>
> Please always include the compiler stderr when fixing build errors or
> warnings.

Ok, will do. With CONFIG_SMP=n and CONFIG_HOTPLUG_CPU=n:

  CC      arch/ia64/kernel/machine_kexec.o
arch/ia64/kernel/machine_kexec.c: In function `machine_shutdown':
arch/ia64/kernel/machine_kexec.c:77: warning: implicit declaration of
function `cpu_down'
  AS      arch/ia64/kernel/relocate_kernel.o
  CC      arch/ia64/kernel/crash.o
arch/ia64/kernel/crash.c: In function `kdump_cpu_freeze':
arch/ia64/kernel/crash.c:139: warning: implicit declaration of
function `ia64_jump_to_sal'
arch/ia64/kernel/crash.c:139: error: `sal_boot_rendez_state'
undeclared (first use in this function)
arch/ia64/kernel/crash.c:139: error: (Each undeclared identifier is
reported only once
arch/ia64/kernel/crash.c:139: error: for each function it appears in.)
arch/ia64/kernel/crash.c: At top level:
arch/ia64/kernel/crash.c:84: warning: 'kdump_wait_cpu_freeze' defined
but not used
make[1]: *** [arch/ia64/kernel/crash.o] Error 1
make: *** [arch/ia64/kernel] Error 2
damm@localhost ~/build/kernel/linux-2.6.20-rc7 $

> > --- 0002/arch/ia64/kernel/crash.c
> > +++ work/arch/ia64/kernel/crash.c     2007-02-01 12:42:38.000000000 +0900
> > @@ -79,6 +79,7 @@ crash_save_this_cpu()
> >       final_note(buf);
> >  }
> >
> > +#ifdef CONFIG_SMP
> >  static int
> >  kdump_wait_cpu_freeze(void)
> >  {
> > @@ -91,6 +92,7 @@ kdump_wait_cpu_freeze(void)
> >       }
> >       return 1;
> >  }
> > +#endif
>
> I think this is a warning fix?

Yes. The file already has some CONFIG_SMP #ifdeffery in it but not
enough to compile properly.

> >  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)

> >  static int
> > --- 0002/arch/ia64/kernel/machine_kexec.c
> > +++ work/arch/ia64/kernel/machine_kexec.c     2007-02-01 12:35:46.000000000 +0900
> > @@ -70,12 +70,14 @@ void machine_kexec_cleanup(struct kimage
> >
> >  void machine_shutdown(void)
> >  {
> > +#ifdef CONFIG_SMP
> >       int cpu;
> >
> >       for_each_online_cpu(cpu) {
> >               if (cpu != smp_processor_id())
> >                       cpu_down(cpu);
> >       }
> > +#endif
> >       kexec_disable_iosapic();
> >  }
>
> hm.  I suspect this one should have been #ifndef CONFIG_HOTPLUG_CPU?

Yes, you are right.
Maybe we can replace the entire code block above with smp_send_stop()
later on? That would make the code more similar to the i386 and x86_64
code.

> I was wondering if we should have stubs for cpu_down() if !CONFIG_HOTPLUG_CPU,
> but perhaps that doesn't make sense.

cpu_down() is only used in a few places so I don't think it's worth it.

I wonder why cpu_down() isn't marked as __cpuexit. Maybe because it is
already wrapped in CONFIG_HOTPLUG_CPU.

Thanks!

/ magnus

RE: [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Zou, Nanhai]

> -----Original Message-----
> From: linux-ia64-owner@vger.kernel.org
> [mailto:linux-ia64-owner@vger.kernel.org] On Behalf Of Magnus Damm
> Sent: 2007年2月2日 10:39
> To: Andrew Morton
> Cc: Magnus Damm; linux-kernel@vger.kernel.org; linux-ia64@vger.kernel.org;
> Luck, Tony; fastboot@lists.osdl.org
> Subject: Re: [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)
> 
> On 2/2/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > (added ia64 list)
> > (added ia64 maintainer)
> > (added kexec list)
> 
> Sorry about that.
> 
> > On Thu, 01 Feb 2007 22:13:47 +0900
> > Magnus Damm <magnus@valinux.co.jp> wrote:
> >
> > > kexec: Fix CONFIG_SMP=n compilation (ia64)
> > >
> > > This patch makes it possible to compile kexec for ia64 without SMP support.
> > >
> >
> > Please always include the compiler stderr when fixing build errors or
> > warnings.
> 
> Ok, will do. With CONFIG_SMP=n and CONFIG_HOTPLUG_CPU=n:
> 
>   CC      arch/ia64/kernel/machine_kexec.o
> arch/ia64/kernel/machine_kexec.c: In function `machine_shutdown':
> arch/ia64/kernel/machine_kexec.c:77: warning: implicit declaration of
> function `cpu_down'
>   AS      arch/ia64/kernel/relocate_kernel.o
>   CC      arch/ia64/kernel/crash.o
> arch/ia64/kernel/crash.c: In function `kdump_cpu_freeze':
> arch/ia64/kernel/crash.c:139: warning: implicit declaration of
> function `ia64_jump_to_sal'
> arch/ia64/kernel/crash.c:139: error: `sal_boot_rendez_state'
> undeclared (first use in this function)
> arch/ia64/kernel/crash.c:139: error: (Each undeclared identifier is
> reported only once
> arch/ia64/kernel/crash.c:139: error: for each function it appears in.)
> arch/ia64/kernel/crash.c: At top level:
> arch/ia64/kernel/crash.c:84: warning: 'kdump_wait_cpu_freeze' defined
> but not used
> make[1]: *** [arch/ia64/kernel/crash.o] Error 1
> make: *** [arch/ia64/kernel] Error 2
> damm@localhost ~/build/kernel/linux-2.6.20-rc7 $
> 
> > > --- 0002/arch/ia64/kernel/crash.c
> > > +++ work/arch/ia64/kernel/crash.c     2007-02-01 12:42:38.000000000
> +0900
> > > @@ -79,6 +79,7 @@ crash_save_this_cpu()
> > >       final_note(buf);
> > >  }
> > >
> > > +#ifdef CONFIG_SMP
> > >  static int
> > >  kdump_wait_cpu_freeze(void)
> > >  {
> > > @@ -91,6 +92,7 @@ kdump_wait_cpu_freeze(void)
> > >       }
> > >       return 1;
> > >  }
> > > +#endif
> >
> > I think this is a warning fix?
> 
> Yes. The file already has some CONFIG_SMP #ifdeffery in it but not
> enough to compile properly.
> 
> > >  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...

Thanks
Zou Nan hai

> 
> Thanks!
> 
> / magnus
> -
> To unsubscribe from this list: send the line "unsubscribe linux-ia64" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [Fastboot] [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Horms]

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...

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

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

Re: [Fastboot] [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Jay Lan]

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

Re: [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Magnus Damm]

On 2/2/07, Magnus Damm <magnus.damm@gmail.com> wrote:
> On 2/2/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> > Magnus Damm <magnus@valinux.co.jp> wrote:
> >
> > > kexec: Fix CONFIG_SMP=n compilation (ia64)
> > >
> > > This patch makes it possible to compile kexec for ia64 without SMP support.
> > > --- 0002/arch/ia64/kernel/machine_kexec.c
> > > +++ work/arch/ia64/kernel/machine_kexec.c     2007-02-01 12:35:46.000000000 +0900
> > > @@ -70,12 +70,14 @@ void machine_kexec_cleanup(struct kimage
> > >
> > >  void machine_shutdown(void)
> > >  {
> > > +#ifdef CONFIG_SMP
> > >       int cpu;
> > >
> > >       for_each_online_cpu(cpu) {
> > >               if (cpu != smp_processor_id())
> > >                       cpu_down(cpu);
> > >       }
> > > +#endif
> > >       kexec_disable_iosapic();
> > >  }
> >
> > hm.  I suspect this one should have been #ifndef CONFIG_HOTPLUG_CPU?

Re-reading this I assume you mean #ifdef CONFIG_HOTPLUG_CPU.

I would be happy to resend a new updated version of the patch, but I
wonder if it may be better to fail miserably during the build than
fail silently in the case of CONFIG_SMP=y but CONFIG_HOTPLUG_CPU=n.

Any ideas?

Nan hai, is there any particular reason why the ia64 kexec code builds
on top of cpu hotplug instead of smp functions such as
smp_send_stop()?

Thanks!

/ magnus

Re: [Fastboot] [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Horms]

On Fri, Feb 02, 2007 at 08:53:00PM +0900, Magnus Damm wrote:
> On 2/2/07, Magnus Damm <magnus.damm@gmail.com> wrote:
> > On 2/2/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> > > Magnus Damm <magnus@valinux.co.jp> wrote:
> > >
> > > > kexec: Fix CONFIG_SMP=n compilation (ia64)
> > > >
> > > > This patch makes it possible to compile kexec for ia64 without SMP support.
> > > > --- 0002/arch/ia64/kernel/machine_kexec.c
> > > > +++ work/arch/ia64/kernel/machine_kexec.c     2007-02-01 12:35:46.000000000 +0900
> > > > @@ -70,12 +70,14 @@ void machine_kexec_cleanup(struct kimage
> > > >
> > > >  void machine_shutdown(void)
> > > >  {
> > > > +#ifdef CONFIG_SMP
> > > >       int cpu;
> > > >
> > > >       for_each_online_cpu(cpu) {
> > > >               if (cpu != smp_processor_id())
> > > >                       cpu_down(cpu);
> > > >       }
> > > > +#endif
> > > >       kexec_disable_iosapic();
> > > >  }
> > >
> > > hm.  I suspect this one should have been #ifndef CONFIG_HOTPLUG_CPU?
> 
> Re-reading this I assume you mean #ifdef CONFIG_HOTPLUG_CPU.
> 
> I would be happy to resend a new updated version of the patch, but I
> wonder if it may be better to fail miserably during the build than
> fail silently in the case of CONFIG_SMP=y but CONFIG_HOTPLUG_CPU=n.

There used to be alternate code for the CONFIG_SMP +
!CONFIG_HOTPLUG_CPU, but this was removed because it was determined to
be flakey and not maintainable (I can dig up the threads if you want).
I think that this means that if we have CONFIG_KEXEC and CONFIG_SMP then
CONFIG_HOTPLUG_CPU is required. I think this is expressable in Kconfig
somehow.

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

RE: [Fastboot] [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Zou, Nanhai]

> -----Original Message-----
> From: Horms [mailto:horms@verge.net.au]
> Sent: 2007年2月3日 11:28
> To: Magnus Damm
> Cc: Andrew Morton; Magnus Damm; Luck, Tony; linux-ia64@vger.kernel.org; Zou,
> Nanhai; fastboot@lists.osdl.org; linux-kernel@vger.kernel.org
> Subject: Re: [Fastboot] [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)
> 
> On Fri, Feb 02, 2007 at 08:53:00PM +0900, Magnus Damm wrote:
> > On 2/2/07, Magnus Damm <magnus.damm@gmail.com> wrote:
> > > On 2/2/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > Magnus Damm <magnus@valinux.co.jp> wrote:
> > > >
> > > > > kexec: Fix CONFIG_SMP=n compilation (ia64)
> > > > >
> > > > > This patch makes it possible to compile kexec for ia64 without SMP
> support.
> > > > > --- 0002/arch/ia64/kernel/machine_kexec.c
> > > > > +++ work/arch/ia64/kernel/machine_kexec.c     2007-02-01
> 12:35:46.000000000 +0900
> > > > > @@ -70,12 +70,14 @@ void machine_kexec_cleanup(struct kimage
> > > > >
> > > > >  void machine_shutdown(void)
> > > > >  {
> > > > > +#ifdef CONFIG_SMP
> > > > >       int cpu;
> > > > >
> > > > >       for_each_online_cpu(cpu) {
> > > > >               if (cpu != smp_processor_id())
> > > > >                       cpu_down(cpu);
> > > > >       }
> > > > > +#endif
> > > > >       kexec_disable_iosapic();
> > > > >  }
> > > >
> > > > hm.  I suspect this one should have been #ifndef CONFIG_HOTPLUG_CPU?
> >
> > Re-reading this I assume you mean #ifdef CONFIG_HOTPLUG_CPU.
> >
> > I would be happy to resend a new updated version of the patch, but I
> > wonder if it may be better to fail miserably during the build than
> > fail silently in the case of CONFIG_SMP=y but CONFIG_HOTPLUG_CPU=n.
> 
> There used to be alternate code for the CONFIG_SMP +
> !CONFIG_HOTPLUG_CPU, but this was removed because it was determined to
> be flakey and not maintainable (I can dig up the threads if you want).
> I think that this means that if we have CONFIG_KEXEC and CONFIG_SMP then
> CONFIG_HOTPLUG_CPU is required. I think this is expressable in Kconfig
> somehow.
> 


Yes, CONFIG_HOTPLUG_CPU is required by Kexec.
But CONFIG_HOTPLUG_CPU is not required by Kdump except SN platform.

Zou Nan hai
> --
> Horms
>   H: http://www.vergenet.net/~horms/
>   W: http://www.valinux.co.jp/en/

Re: [Fastboot] [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)

[Magnus Damm]

On 2/3/07, Horms <horms@verge.net.au> wrote:
> On Fri, Feb 02, 2007 at 08:53:00PM +0900, Magnus Damm wrote:
> > On 2/2/07, Magnus Damm <magnus.damm@gmail.com> wrote:
> > > On 2/2/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > Magnus Damm <magnus@valinux.co.jp> wrote:
> > > >
> > > > > kexec: Fix CONFIG_SMP=n compilation (ia64)
> > > > >
> > > > > This patch makes it possible to compile kexec for ia64 without SMP support.
> > > > > --- 0002/arch/ia64/kernel/machine_kexec.c
> > > > > +++ work/arch/ia64/kernel/machine_kexec.c     2007-02-01 12:35:46.000000000 +0900
> > > > > @@ -70,12 +70,14 @@ void machine_kexec_cleanup(struct kimage
> > > > >
> > > > >  void machine_shutdown(void)
> > > > >  {
> > > > > +#ifdef CONFIG_SMP
> > > > >       int cpu;
> > > > >
> > > > >       for_each_online_cpu(cpu) {
> > > > >               if (cpu != smp_processor_id())
> > > > >                       cpu_down(cpu);
> > > > >       }
> > > > > +#endif
> > > > >       kexec_disable_iosapic();
> > > > >  }
> > > >
> > > > hm.  I suspect this one should have been #ifndef CONFIG_HOTPLUG_CPU?
> >
> > Re-reading this I assume you mean #ifdef CONFIG_HOTPLUG_CPU.
> >
> > I would be happy to resend a new updated version of the patch, but I
> > wonder if it may be better to fail miserably during the build than
> > fail silently in the case of CONFIG_SMP=y but CONFIG_HOTPLUG_CPU=n.
>
> There used to be alternate code for the CONFIG_SMP +
> !CONFIG_HOTPLUG_CPU, but this was removed because it was determined to
> be flakey and not maintainable (I can dig up the threads if you want).
> I think that this means that if we have CONFIG_KEXEC and CONFIG_SMP then
> CONFIG_HOTPLUG_CPU is required. I think this is expressable in Kconfig
> somehow.

My mistake, the following lines from linux-2.6.20/arch/ia64/Kconfig
seem to handle this case already:

config KEXEC
	bool "kexec system call (EXPERIMENTAL)"
	depends on EXPERIMENTAL && !IA64_HP_SIM && (!SMP || HOTPLUG_CPU)

I'll send an updated patch in a short while. Thanks!

/ magnus