[PATCH] Check for online cpus before bringing them up

[Srivatsa Vaddagiri <vatsa@in.ibm.com>]

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>

-

 arch/i386/kernel/smpboot.c |    6 ++++++
 1 files changed, 6 insertions(+)

diff -puN arch/i386/kernel/smpboot.c~cpuhp arch/i386/kernel/smpboot.c
--- linux-2.6.16-rc5/arch/i386/kernel/smpboot.c~cpuhp	2006-03-14 14:42:26.000000000 +0530
+++ linux-2.6.16-rc5-root/arch/i386/kernel/smpboot.c	2006-03-14 14:43:21.000000000 +0530
@@ -1029,6 +1029,12 @@ int __devinit smp_prepare_cpu(int cpu)
 	int	apicid, ret;
 
 	lock_cpu_hotplug();
+
+	if (cpu_online(cpu)) {
+		ret = -EINVAL;
+		goto exit;
+	}
+
 	apicid = x86_cpu_to_apicid[cpu];
 	if (apicid == BAD_APICID) {
 		ret = -ENODEV;

_


-- 
Regards,
vatsa