nommu: fix a number of issues with the per-MM VMA patch

Fix a number of issues with the per-MM VMA patch:

 (1) Make mmap_pages_allocated an atomic_long_t, just in case this is used on
     a NOMMU system with more than 2G pages.  Makes no difference on a 32-bit
     system.

 (2) Report vma->vm_pgoff * PAGE_SIZE as a 64-bit value, not a 32-bit value,
     lest it overflow.

 (3) Move the allocation of the vm_area_struct slab back for fork.c.

 (4) Use KMEM_CACHE() for both vm_area_struct and vm_region slabs.

 (5) Use BUG_ON() rather than if () BUG().

 (6) Make the default validate_nommu_regions() a static inline rather than a
     #define.

 (7) Make free_page_series()'s objection to pages with a refcount != 1 more
     informative.

 (8) Adjust the __put_nommu_region() banner comment to indicate that the
     semaphore must be held for writing.

 (9) Limit the number of warnings about munmaps of non-mmapped regions.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -2481,7 +2481,4 @@ void mm_drop_all_locks(struct mm_struct *mm)
  */
 void __init mmap_init(void)
 {
-	vm_area_cachep = kmem_cache_create("vm_area_struct",
-			sizeof(struct vm_area_struct), 0,
-			SLAB_PANIC, NULL);
 }