linux-kernel - Re: 2.6.28-rc6: early panic with boot option "nosmp"

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Message-ID: <493846E1.7010104@kernel.org>
Date:	Thu, 04 Dec 2008 13:08:49 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jack Steiner <steiner@....com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 2.6.28-rc6: early panic with boot option "nosmp"

Ingo Molnar wrote:
> * Andi Kleen <andi@...stfloor.org> wrote:
> 
>>> The exception raised on dereferencing mpf or mpf_found.
>> This obvious patch should fix it then. Does it?
>>
>> --
>>
>> Fix early exception in __get_smp_config with nosmp
>>
>> Bail out early when there is no MP table.
>>
>> Reported by Wu Fengguang
>> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
>>
>> ---
>>  arch/x86/kernel/mpparse.c |    3 +++
>>  1 file changed, 3 insertions(+)
> 
> applied to tip/x86/urgent, thanks Andi!
> 

looks like his system doesn't have mps table.
and when maxcpus=0, or nosmp will cause skip_ioapic_setup = 1, and acpi_ioapic = 0

but smp_found_config is set acpi_boot_init.. with madt.

could move that check earlier

diff --git a/arch/x86/kernel/mpparse.c b/arch/x86/kernel/mpparse.c
index 0f4c1fd..18f90af 100644
--- a/arch/x86/kernel/mpparse.c
+++ b/arch/x86/kernel/mpparse.c
@@ -586,6 +586,9 @@ static void __init __get_smp_config(unsigned int early)
 {
 	struct intel_mp_floating *mpf = mpf_found;
 
+	if (!mpf)
+		return;
+
 	if (x86_quirks->mach_get_smp_config) {
 		if (x86_quirks->mach_get_smp_config(early))
 			return;
@@ -604,9 +607,6 @@ static void __init __get_smp_config(unsigned int early)
 		printk(KERN_INFO "Using ACPI for processor (LAPIC) "
 		       "configuration information\n");
 
-	if (!mpf)
-		return;
-
 	printk(KERN_INFO "Intel MultiProcessor Specification v1.%d\n",
 	       mpf->mpf_specification);
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86_32)



YH
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