[PATCH] x86_64: add nmi_exit to die_nmi

[Corey Minyard]

Playing with NMI watchdog on x86_64, I discovered that it didn't
do what I expected.  It always panic-ed, even when it didn't
happen from interrupt context.  This patch solves that
problem for me.  Also, in this case, do_exit() will be called
with interrupts disabled, I believe.  Would it be wise to also
call local_irq_enable() after nmi_exit()?

Currently, on x86_64, any NMI watchdog timeout will cause a panic
because the irq count will always be set to be in an interrupt
when do_exit() is called from die_nmi().  If we add nmi_exit() to 
the die_nmi() call (since the nmi will never exit "normally")
it seems to solve this problem.  The following small program
can be used to trigger the NMI watchdog to reproduce this:
  main ()
  {
        iopl(3);
        for (;;) asm("cli");
  }

diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 0ebb281..872ddfc 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -472,6 +472,7 @@ void __kprobes die_nmi(char *str, struct
 		panic("nmi watchdog");
 	printk("console shuts up ...\n");
 	oops_end(flags);
+	nmi_exit();
 	do_exit(SIGSEGV);
 }
 
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