[PATCH v3 3/5] x86: fix list corruption on CPU hotplug

[Igor Mammedov <imammedo@redhat.com>]

currently if AP wake up is failed, master CPU marks AP as not present
in do_boot_cpu() by calling set_cpu_present(cpu, false).
That leads to following list corruption on the next physical CPU
hotplug:

[  418.107336] WARNING: CPU: 1 PID: 45 at lib/list_debug.c:33 __list_add+0xbe/0xd0()
[  418.115268] list_add corruption. prev->next should be next (ffff88003dc57600), but was ffff88003e20c3a0. (prev=ffff88003e20c3a0).
[  418.123693] Modules linked in: nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6t_REJECT ipt_REJECT cfg80211 xt_conntrack rfkill ee
[  418.138979] CPU: 1 PID: 45 Comm: kworker/u10:1 Not tainted 3.14.0-rc6+ #387
[  418.149989] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007
[  418.165750] Workqueue: kacpi_hotplug acpi_hotplug_work_fn
[  418.166433]  0000000000000021 ffff880038ca7988 ffffffff8159b22d 0000000000000021
[  418.176460]  ffff880038ca79d8 ffff880038ca79c8 ffffffff8106942c ffff880038ca79e8
[  418.177453]  ffff88003e20c3a0 ffff88003dc57600 ffff88003e20c3a0 00000000ffffffea
[  418.178445] Call Trace:
[  418.185811]  [<ffffffff8159b22d>] dump_stack+0x49/0x5c
[  418.186440]  [<ffffffff8106942c>] warn_slowpath_common+0x8c/0xc0
[  418.187192]  [<ffffffff81069516>] warn_slowpath_fmt+0x46/0x50
[  418.191231]  [<ffffffff8136ef51>] ? acpi_ns_get_node+0xb7/0xc7
[  418.193889]  [<ffffffff812f796e>] __list_add+0xbe/0xd0
[  418.196649]  [<ffffffff812e2aa9>] kobject_add_internal+0x79/0x200
[  418.208610]  [<ffffffff812e2e18>] kobject_add_varg+0x38/0x60
[  418.213831]  [<ffffffff812e2ef4>] kobject_add+0x44/0x70
[  418.229961]  [<ffffffff813e2c60>] device_add+0xd0/0x550
[  418.234991]  [<ffffffff813f0e95>] ? pm_runtime_init+0xe5/0xf0
[  418.250226]  [<ffffffff813e32be>] device_register+0x1e/0x30
[  418.255296]  [<ffffffff813e82a3>] register_cpu+0xe3/0x130
[  418.266539]  [<ffffffff81592be5>] arch_register_cpu+0x65/0x150
[  418.285845]  [<ffffffff81355c0d>] acpi_processor_hotadd_init+0x5a/0x9b
...
Which is caused by the fact that generic_processor_info() allocates
logical CPU id by calling:

 cpu = cpumask_next_zero(-1, cpu_present_mask);

which returns id of previously failed to wake up CPU, since its bit
is cleared by do_boot_cpu() and as result register_cpu() tries to
register another CPU with the same id as already present but failed
to be onlined CPU.

Taking in account that AP will not do anything if master CPU failed to
wake it up, there is no reason to mark that AP as not present and
break next cpu hotplug attempts. As a side effect of not marking AP
as not present, user would be allowed to online it again later.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 arch/x86/kernel/smpboot.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 853473d..e7c15d7 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -822,7 +822,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 			schedule();
 		}
 	} else {
-		set_cpu_present(cpu, false);
 		per_cpu(x86_cpu_to_apicid, cpu) = BAD_APICID;
 	}
 
-- 
1.7.1