linux-kernel - Re: 2.6.27rc1 cannot boot more than 8CPUs

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Date:	Mon, 11 Aug 2008 22:44:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	Jeff Chua <jeff.chua.linux@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Li Zefan <lizf@...fujitsu.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.27rc1 cannot boot more than 8CPUs


* Yinghai Lu <yhlu.kernel@...il.com> wrote:

> [PATCH] x86: move def_to_bigsmp check later
> 
> and skip the apicid id > 8

applied to tip/x86/urgent - thanks Yinghai. While we are touching this 
code i cleaned up the printk a bit: the line breaking was way too ugly, 
and the message not very informative about the effects of this problem. 
See the full commit below.

	Ingo

--------------->
>From b74548e76a0eab1f29546e7c5a589429c069a680 Mon Sep 17 00:00:00 2001
From: Yinghai Lu <yhlu.kernel@...il.com>
Date: Mon, 11 Aug 2008 13:36:04 -0700
Subject: [PATCH] x86: fix 2.6.27rc1 cannot boot more than 8CPUs

Jeff Chua reported that booting a !bigsmp kernel on a 16-way box
hangs silently.

this is a long-standing issue, smp start AP cpu could check the
apic id >=8 etc before trying to start it.

achieve this by moving the def_to_bigsmp check later and skip the
apicid id > 8

[ mingo@...e.hu: clean up the message that is printed. ]

Reported-by: "Jeff Chua" <jeff.chua.linux@...il.com>
Signed-off-by: Yinghai Lu <yhlu.kernel@...il.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>

 arch/x86/kernel/setup.c   |    6 ------
 arch/x86/kernel/smpboot.c |   10 ++++++++++
 2 files changed, 10 insertions(+), 6 deletions(-)
---
 arch/x86/kernel/setup.c   |    6 ------
 arch/x86/kernel/smpboot.c |   10 ++++++++++
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 6e5823b..68b48e3 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -861,12 +861,6 @@ void __init setup_arch(char **cmdline_p)
 	init_apic_mappings();
 	ioapic_init_mappings();
 
-#if defined(CONFIG_SMP) && defined(CONFIG_X86_PC) && defined(CONFIG_X86_32)
-	if (def_to_bigsmp)
-		printk(KERN_WARNING "More than 8 CPUs detected and "
-			"CONFIG_X86_PC cannot handle it.\nUse "
-			"CONFIG_X86_GENERICARCH or CONFIG_X86_BIGSMP.\n");
-#endif
 	kvm_guest_init();
 
 	e820_reserve_resources();
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index da10f07..91055d7 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -994,7 +994,17 @@ int __cpuinit native_cpu_up(unsigned int cpu)
 	flush_tlb_all();
 	low_mappings = 1;
 
+#ifdef CONFIG_X86_PC
+	if (def_to_bigsmp && apicid > 8) {
+		printk(KERN_WARNING
+			"More than 8 CPUs detected - skipping them.\n"
+			"Use CONFIG_X86_GENERICARCH and CONFIG_X86_BIGSMP.\n");
+		err = -1;
+	} else
+		err = do_boot_cpu(apicid, cpu);
+#else
 	err = do_boot_cpu(apicid, cpu);
+#endif
 
 	zap_low_mappings();
 	low_mappings = 0;
--
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