x86/smp: Add irq_enter/exit() in smp_reschedule_interrupt()

 ===============================
 [ INFO: suspicious RCU usage. ]
 4.8.0+ hardkernel#24 Not tainted
 -------------------------------
 ./arch/x86/include/asm/msr-trace.h:47 suspicious rcu_dereference_check() usage!
 
 other info that might help us debug this:
 
 RCU used illegally from idle CPU!
 rcu_scheduler_active = 1, debug_locks = 0
 RCU used illegally from extended quiescent state!
 no locks held by swapper/1/0.
 
  [<ffffffff9d492b95>] do_trace_write_msr+0x135/0x140
  [<ffffffff9d06f860>] native_write_msr+0x20/0x30
  [<ffffffff9d065fad>] native_apic_msr_eoi_write+0x1d/0x30
  [<ffffffff9d05bd1d>] smp_reschedule_interrupt+0x1d/0x30
  [<ffffffff9d8daec6>] reschedule_interrupt+0x96/0xa0

Reschedule interrupt may be called in cpu idle state. This causes lockdep 
check warning above. 

Add irq_enter/exit() in smp_reschedule_interrupt(), irq_enter() tells the RCU 
subsystems to end the extended quiescent state, so the following trace call in 
ack_APIC_irq() works correctly.

Signed-off-by: Wanpeng Li <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Mike Galbraith <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

arch/x86/kernel/smp.c

@@ -259,8 +259,10 @@ static inline void __smp_reschedule_interrupt(void)
 
 __visible void smp_reschedule_interrupt(struct pt_regs *regs)
 {
+	irq_enter();
 	ack_APIC_irq();
 	__smp_reschedule_interrupt();
+	irq_exit();
 	/*
 	 * KVM uses this interrupt to force a cpu out of guest mode
 	 */