[PATCH] CPU hotplug: call check_tsc_sync_source() with irqs off

check_tsc_sync_source() depends on being called with irqs disabled (it
checks whether the TSC is coherent across two specific CPUs). This is
incidentally true during bootup, but not during cpu hotplug __cpu_up().
This got found via smp_processor_id() debugging.

disable irqs explicitly and remove the unconditional enabling of
interrupts. Add touch_nmi_watchdog() to the cpu_online_map busy loop.

this bug is present both on i386 and on x86_64.

Reported-by: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
index 35443729aad8..cd4643a37022 100644
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -923,8 +923,9 @@ void __init smp_prepare_boot_cpu(void)
  */
 int __cpuinit __cpu_up(unsigned int cpu)
 {
-        int err;
         int apicid = cpu_present_to_apicid(cpu);
+        unsigned long flags;
+        int err;
 
         WARN_ON(irqs_disabled());
 
@@ -958,7 +959,9 @@ int __cpuinit __cpu_up(unsigned int cpu)
         /*
          * Make sure and check TSC sync:
          */
+        local_irq_save(flags);
         check_tsc_sync_source(cpu);
+        local_irq_restore(flags);
 
         while (!cpu_isset(cpu, cpu_online_map))
                 cpu_relax();