[PATCH] ppc64: Fix CPU hot unplug deadlock

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>

My RTAS locking fixes incorrectly added a spinlock around the function used
to stop a CPU, that function never returns, thus the lock becomes stale.
The correct fix is to disable interrupts instead (the RTAS params beeing
per-CPU, this should be safe enough)

arch/ppc64/kernel/rtas.c

@@ -504,9 +504,9 @@ asmlinkage int ppc_rtas(struct rtas_args __user *uargs)
 void rtas_stop_self(void)
 {
 	struct rtas_args *rtas_args = &(get_paca()->xRtas);
-	unsigned long s;
 
-	spin_lock_irqsave(&rtas.lock, s);
+	local_irq_disable(s);
+
 	rtas_args->token = rtas_token("stop-self");
 	BUG_ON(rtas_args->token == RTAS_UNKNOWN_SERVICE);
 	rtas_args->nargs = 0;
@@ -516,7 +516,6 @@ void rtas_stop_self(void)
 	printk("%u %u Ready to die...\n",
 	       smp_processor_id(), hard_smp_processor_id());
 	enter_rtas((void *)__pa(rtas_args));
-	spin_unlock_irqrestore(&rtas.lock, s);
 
 	panic("Alas, I survived.\n");
 }