Recursive deadlock on die_lock

[Keith Owens <kaos@ocs.com.au>]

Typical die() code.

spinlock_t die_lock = SPIN_LOCK_UNLOCKED;

void die(const char * str, struct pt_regs * regs, long err)
{
        console_verbose();
        spin_lock_irq(&die_lock);
        bust_spinlocks(1);
        printk("%s: %04lx\n", str, err & 0xffff);
        show_registers(regs);
        bust_spinlocks(0);
        spin_unlock_irq(&die_lock);
        do_exit(SIGSEGV);
}

If show_registers() fails (which it does far too often on IA64) then
the system deadlocks trying to recursively obtain die_lock.  Also
die_lock is never used outside die(), it should be proc local.
Suggested fix:

void die(const char * str, struct pt_regs * regs, long err)
{
	static spinlock_t die_lock = SPIN_LOCK_UNLOCKED;
	static int die_lock_owner = -1, die_lock_owner_depth = 0;

	if (die_lock_owner != smp_processor_id()) {
		console_verbose();
		spin_lock_irq(&die_lock);
		die_lock_owner = smp_processor_id();
		die_lock_owner_depth = 0;
		bust_spinlocks(1);
	}

	if (++die_lock_owner_depth < 3) {
		printk("%s: %04lx\n", str, err & 0xffff);
		show_registers(regs);
	}
	else
		printk(KERN_ERR "Recursive die() failure, registers suppressed\n");

	bust_spinlocks(0);
	die_lock_owner = -1;
	spin_unlock_irq(&die_lock);
        do_exit(SIGSEGV);
}