linux-kernel - Re: [PATCH] x86: fix cpu-hotplug regression

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Date:	Wed, 7 Nov 2007 14:18:36 +0100
From:	"Andreas Herrmann" <andreas.herrmann3@....com>
To:	"Andi Kleen" <ak@...e.de>
cc:	"Thomas Gleixner" <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org,
	"Akinobu Mita" <akinobu.mita@...il.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86: fix cpu-hotplug regression

On Wed, Nov 07, 2007 at 03:35:43AM +0100, Andi Kleen wrote:
> On Wednesday 07 November 2007 02:12, Andreas Herrmann wrote:
> 
> > In cases where not all CPUs are brought up during
> > boot (e.g. using maxcpus and additional_cpus parameters)
> > mce_cpu_callback now returns NOTFIY_BAD because
> > for such CPUs cpu_data is not completely filled when
> > the notifier is called. Thus mce_create_device fails right
> > at its beginning:
> >
> >         if (!mce_available(&cpu_data[cpu]))
> >                 return -EIO;
> >
> > As a quick fix I suggest to check boot_cpu_data for MCE.
> 
> I guess it would be better to just move the device creation
> to after the CPU has booted. AKA call mce_create_dev() on CPU_ONLINE
> instead.

Yes, and this was the old behaviour. The mentioned patch changed it -
("do mce_create_device in CPU_UP_PREPARE instead of CPU_ONLINE").

Thinking twice about the problem it seems obvious that this part
of the patch should just be reverted.

Attached is a new fix (diff against 2.6.24-rc2).


Regards,

Andreas

--
[PATCH] x86: fix cpu hotplug regression (don't call mce_create_device on CPU_UP_PREPARE)

Fix regression introduced with d435d862baca3e25e5eec236762a43251b1e7ffc
("cpu hotplug: mce: fix cpu hotplug error handling").

For CPUs not brought up during boot (using maxcpus and additional_cpus
parameters) we don't know whether mce is supported or not at "CPU_UP_PREPARE"-time.
Thus mce_cpu_callback should be called after the CPU is online.


Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>
---
 arch/x86/kernel/cpu/mcheck/mce_64.c |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_64.c b/arch/x86/kernel/cpu/mcheck/mce_64.c
index b9f802e..8e83070 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_64.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_64.c
@@ -855,12 +855,10 @@ mce_cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 	int err = 0;
 
 	switch (action) {
-	case CPU_UP_PREPARE:
-	case CPU_UP_PREPARE_FROZEN:
+	case CPU_ONLINE:
+	case CPU_ONLINE_FROZEN:
 		err = mce_create_device(cpu);
 		break;
-	case CPU_UP_CANCELED:
-	case CPU_UP_CANCELED_FROZEN:
 	case CPU_DEAD:
 	case CPU_DEAD_FROZEN:
 		mce_remove_device(cpu);
-- 
1.5.3.4




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