From 82c3c03a4096badd026c6e337f3c5dde020e9ec6 Mon Sep 17 00:00:00 2001 From: Srivatsa Vaddagiri Date: Thu, 16 Mar 2006 23:04:06 -0800 Subject: [PATCH] [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/i386/kernel/smpboot.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c index eba7f53f8b4a..7007e1783797 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; -- 2.39.5