badpage: zap print_bad_pte on swap and file

Complete zap_pte_range()'s coverage of bad pagetable entries by calling
print_bad_pte() on a pte_file in a linear vma and on a bad swap entry.
That needs free_swap_and_cache() to tell it, which will also have shown
one of those "swap_free" errors (but with much less information).

Similar checks in fork's copy_one_pte()?  No, that would be more noisy
than helpful: we'll see them when parent and child exec or exit.

Where do_nonlinear_fault() calls print_bad_pte(): omit !VM_CAN_NONLINEAR
case, that could only be a bug in sys_remap_file_pages(), not a bad pte.
VM_FAULT_OOM rather than VM_FAULT_SIGBUS?  Well, okay, that is consistent
with what happens if do_swap_page() operates a bad swap entry; but don't
we have patches to be more careful about killing when VM_FAULT_OOM?

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swapfile.c

@@ -571,13 +571,13 @@ int try_to_free_swap(struct page *page)
  * Free the swap entry like above, but also try to
  * free the page cache entry if it is the last user.
  */
-void free_swap_and_cache(swp_entry_t entry)
+int free_swap_and_cache(swp_entry_t entry)
 {
-	struct swap_info_struct * p;
+	struct swap_info_struct *p;
 	struct page *page = NULL;
 
 	if (is_migration_entry(entry))
-		return;
+		return 1;
 
 	p = swap_info_get(entry);
 	if (p) {
@@ -603,6 +603,7 @@ void free_swap_and_cache(swp_entry_t entry)
 		unlock_page(page);
 		page_cache_release(page);
 	}
+	return p != NULL;
 }
 
 #ifdef CONFIG_HIBERNATION