mm/page_io.c: replace some BUG_ON()s with VM_BUG_ON_PAGE()

So they are CONFIG_DEBUG_VM-only and more informative.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Joe Perches <joe@perches.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Rik van Riel <riel@redhat.com>
Cc: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_io.c

@@ -264,7 +264,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 	int ret;
 	struct swap_info_struct *sis = page_swap_info(page);
 
-	BUG_ON(!PageSwapCache(page));
+	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 	if (sis->flags & SWP_FILE) {
 		struct kiocb kiocb;
 		struct file *swap_file = sis->swap_file;
@@ -338,7 +338,7 @@ int swap_readpage(struct page *page)
 	int ret = 0;
 	struct swap_info_struct *sis = page_swap_info(page);
 
-	BUG_ON(!PageSwapCache(page));
+	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(PageUptodate(page), page);
 	if (frontswap_load(page) == 0) {
@@ -388,7 +388,8 @@ int swap_set_page_dirty(struct page *page)
 
 	if (sis->flags & SWP_FILE) {
 		struct address_space *mapping = sis->swap_file->f_mapping;
-		BUG_ON(!PageSwapCache(page));
+
+		VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 		return mapping->a_ops->set_page_dirty(page);
 	} else {
 		return __set_page_dirty_no_writeback(page);