slab,slub: don't enable interrupts during early boot

As explained by Benjamin Herrenschmidt:

  Oh and btw, your patch alone doesn't fix powerpc, because it's missing
  a whole bunch of GFP_KERNEL's in the arch code... You would have to
  grep the entire kernel for things that check slab_is_available() and
  even then you'll be missing some.

  For example, slab_is_available() didn't always exist, and so in the
  early days on powerpc, we used a mem_init_done global that is set form
  mem_init() (not perfect but works in practice). And we still have code
  using that to do the test.

Therefore, mask out __GFP_WAIT, __GFP_IO, and __GFP_FS in the slab allocators
in early boot code to avoid enabling interrupts.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

init/main.c

@@ -640,6 +640,7 @@ asmlinkage void __init start_kernel(void)
 				 "enabled early\n");
 	early_boot_irqs_on();
 	local_irq_enable();
+	kmem_cache_init_late();
 
 	/*
 	 * HACK ALERT! This is early. We're enabling the console before