[PATCH 2/3] x86: halt secondary CPU if master doesn't wait on it

[Igor Mammedov <imammedo@redhat.com>]

if during CPU hotplug master CPU had errors during
sending AP wake up IPIs, it fails hotplug operation.
But AP might start and spin on never set
cpu_callout_mask indefinitely, consuming power or
host VCPU resources needlessly.

On the other hand, master CPU marks AP with
BAD_APICID if hotplug attempt failed, so use this
fact to halt CPU to avoid needless spinning.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 arch/x86/kernel/cpu/common.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index e048e87..9f07b8e 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1242,8 +1242,11 @@ void cpu_init(void)
 	 * wait till the master CPU completes it's STARTUP sequence,
 	 * and decides to wait till this AP boots
 	 */
-	while (!cpumask_test_cpu(cpu, cpu_callout_mask))
+	while (!cpumask_test_cpu(cpu, cpu_callout_mask)) {
 		cpu_relax();
+		if (per_cpu(x86_cpu_to_apicid, cpu) == BAD_APICID)
+			halt();
+	}
 
 	/*
 	 * Load microcode on this cpu if a valid microcode is available.
@@ -1345,8 +1348,11 @@ void cpu_init(void)
 	 * wait till the master CPU completes it's STARTUP sequence,
 	 * and decides to wait till this AP boots
 	 */
-	while (!cpumask_test_cpu(cpu, cpu_callout_mask))
+	while (!cpumask_test_cpu(cpu, cpu_callout_mask)) {
 		cpu_relax();
+		if (per_cpu(x86_cpu_to_apicid, cpu) == BAD_APICID)
+			halt();
+	}
 
 
 	show_ucode_info_early();
-- 
1.7.1