[PATCH] Fix GFP_HIGHMEM slab panic

As reported by Martin J. Bligh <mbligh@google.com>, we let through some
non-slab bits to slab allocation through __get_vm_area_node when doing a
vmalloc.

I haven't been able to reproduce this, although I understand why it
happens: vmalloc allocates memory with

GFP_KERNEL | __GFP_HIGHMEM

and commit 52fd24ca resulted in the same
flags are passed down to cache_alloc_refill, causing the BUG.  The
following patch fixes it.

Note that when calling kmalloc_node, I am masking off __GFP_HIGHMEM with
GFP_LEVEL_MASK, whereas __vmalloc_area_node does the same with

~(__GFP_HIGHMEM | __GFP_ZERO).

IMHO, using GFP_LEVEL_MASK is preferable, but either should fix this
problem.

Signed-off-by: Giridhar Pemmasani (pgiri@yahoo.com)
Cc: Martin J. Bligh <mbligh@google.com>
Cc: Andrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/vmalloc.c

@@ -182,7 +182,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size, unsigned long fl
 	addr = ALIGN(start, align);
 	size = PAGE_ALIGN(size);
 
-	area = kmalloc_node(sizeof(*area), gfp_mask, node);
+	area = kmalloc_node(sizeof(*area), gfp_mask & GFP_LEVEL_MASK, node);
 	if (unlikely(!area))
 		return NULL;