[PATCH 2/2] x86, reschedule: check to see if system is shutting down

[Don Zickus <dzickus@redhat.com>]

Due to reschedule changes in v3.3, a WARN_ON has popped up
because a cpu suddenly became offline without letting anyone
know.

This results in the schedule trying to move something to another
cpu only to find out it isn't there and getting confused.  The splat
looks something like:

[   32.448626] ------------[ cut here ]------------
[   32.449160] WARNING: at arch/x86/kernel/smp.c:119 native_smp_send_reschedule+0x25/0x43()
[   32.449621] Pid: 1, comm: init_stage2 Not tainted 3.2.0+ #14
[   32.449621] Call Trace:
[   32.449621]  <IRQ>  [<ffffffff81041a44>] ? native_smp_send_reschedule+0x25/0x43
[   32.449621]  [<ffffffff810735b2>] warn_slowpath_common+0x7b/0x93
[   32.449621]  [<ffffffff810962cc>] ? tick_nohz_handler+0xc9/0xc9
[   32.449621]  [<ffffffff81073675>] warn_slowpath_null+0x15/0x18
[   32.449621]  [<ffffffff81041a44>] native_smp_send_reschedule+0x25/0x43
[   32.449621]  [<ffffffff81067a00>] smp_send_reschedule+0xa/0xc
[   32.449621]  [<ffffffff8106f25e>] scheduler_tick+0x21a/0x242
[   32.449621]  [<ffffffff8107da10>] update_process_times+0x62/0x73
[   32.449621]  [<ffffffff81096336>] tick_sched_timer+0x6a/0x8a
[   32.449621]  [<ffffffff8108c5eb>] __run_hrtimer.clone.26+0x55/0xcb
[   32.449621]  [<ffffffff8108cd77>] hrtimer_interrupt+0xcb/0x19b
[   32.449621]  [<ffffffff810428a8>] smp_apic_timer_interrupt+0x72/0x85
[   32.449621]  [<ffffffff8165a8de>] apic_timer_interrupt+0x6e/0x80
[   32.449621]  <EOI>  [<ffffffff8165928e>] ? _raw_spin_unlock_irqrestore+0x3a/0x3e
[   32.449621]  [<ffffffff81042f4e>] ? arch_local_irq_restore+0x6/0xd
[   32.449621]  [<ffffffff810430c4>] default_send_IPI_mask_allbutself_phys+0x78/0x88
[   32.449621]  [<ffffffff8106c3c4>] ? __migrate_task+0xf1/0xf1
[   32.449621]  [<ffffffff81045445>] physflat_send_IPI_allbutself+0x12/0x14
[   32.449621]  [<ffffffff81041aaf>] native_stop_other_cpus+0x4d/0xa8
[   32.449621]  [<ffffffff810411c6>] native_machine_shutdown+0x56/0x6d
[   32.449621]  [<ffffffff81048499>] kvm_shutdown+0x1a/0x1c
[   32.449621]  [<ffffffff810411f9>] machine_shutdown+0xa/0xc
[   32.449621]  [<ffffffff81041265>] native_machine_restart+0x20/0x32
[   32.449621]  [<ffffffff81041297>] machine_restart+0xa/0xc
[   32.449621]  [<ffffffff81081d53>] kernel_restart+0x49/0x4d

I solved this by re-using the atomic global variable that is set during
native_smp_stop_other_cpus().  This is the piece of code that causes the
problem and it sets stopping_cpu to reflect the system is going down.

If the variable is set do not yell with the WARN_ON, just return.

v2:  use if-condition for WARN-ON instead of if {WARN_ON(1)}

Signed-off-by: Don Zickus <dzickus@redhat.com>
---
 arch/x86/kernel/smp.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 48d2b7d..54d570e 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -120,7 +120,8 @@ static bool smp_no_nmi_ipi = false;
 static void native_smp_send_reschedule(int cpu)
 {
 	if (unlikely(cpu_is_offline(cpu))) {
-		WARN_ON(1);
+		/* system is not shutting down.. yell */
+		WARN_ON(atomic_read(&stopping_cpu) == -1)
 		return;
 	}
 	apic->send_IPI_mask(cpumask_of(cpu), RESCHEDULE_VECTOR);
-- 
1.7.7.6