powerpc/mm: Fix SMP issue with MMU context handling code

In switch_mmu_context() if we call steal_context_smp() to get a context
to use we shouldn't fall through and than call steal_context_up().  Doing
so can be problematic in that the 'mm' that steal_context_up() ends up
using will not get marked dirty in the stale_map[] for other CPUs that
might have used that mm.  Thus we could end up with stale TLB entries in
the other CPUs that can cause all kinda of havoc.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/mm/mmu_context_nohash.c

@@ -217,6 +217,7 @@ void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
 			id = steal_context_smp(id);
 			if (id == MMU_NO_CONTEXT)
 				goto again;
+			goto stolen;
 		}
 #endif /* CONFIG_SMP */
 		id = steal_context_up(id);