From 82c3c03a4096badd026c6e337f3c5dde020e9ec6 Mon Sep 17 00:00:00 2001
From: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Date: Thu, 16 Mar 2006 23:04:06 -0800
Subject: [PATCH] x86: check for online cpus before bringing them up

Bryce reported a bug wherein offlining CPU0 (on x86 box) and then
subsequently onlining it resulted in a lockup.

On x86, CPU0 is never offlined.  The subsequent attempt to online CPU0
doesn't take that into account.  It actually tries to bootup the already
booted CPU.  Following patch fixes the problem (as acknowledged by Bryce).
Please consider for inclusion in 2.6.16.

Check if cpu is already online.

Signed-off-by: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
 arch/i386/kernel/smpboot.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'arch')

diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index eba7f53..7007e17 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -1029,6 +1029,16 @@ int __devinit smp_prepare_cpu(int cpu)
 	int	apicid, ret;
 
 	lock_cpu_hotplug();
+
+	/*
+	 * On x86, CPU0 is never offlined.  Trying to bring up an
+	 * already-booted CPU will hang.  So check for that case.
+	 */
+	if (cpu_online(cpu)) {
+		ret = -EINVAL;
+		goto exit;
+	}
+
 	apicid = x86_cpu_to_apicid[cpu];
 	if (apicid == BAD_APICID) {
 		ret = -ENODEV;
-- 
cgit v1.1