[PATCH] blk_run_page() race fix

blk_run_page() is incorrectly using page->mapping, which makes it racy against
removal from swapcache.

Make block_sync_page() use page_mapping(), and remove bkl_run_page(), which
only had one caller.

fs/buffer.c

@@ -2960,7 +2960,12 @@ EXPORT_SYMBOL(try_to_free_buffers);
 
 int block_sync_page(struct page *page)
 {
-	blk_run_page(page);
+	struct address_space *mapping;
+
+	smp_mb();
+	mapping = page_mapping(page);
+	if (mapping)
+		blk_run_backing_dev(mapping->backing_dev_info, page);
 	return 0;
 }
 

include/linux/blkdev.h

@@ -545,16 +545,6 @@ static inline void blk_run_address_space(struct address_space *mapping)
 		blk_run_backing_dev(mapping->backing_dev_info, NULL);
 }
 
-static inline void blk_run_page(struct page *page)
-{
-	struct address_space *mapping;
-
-	smp_mb();
-	mapping = page->mapping;
-	if (mapping)
-		blk_run_backing_dev(mapping->backing_dev_info, page);
-}
-
 /*
  * end_request() and friends. Must be called with the request queue spinlock
  * acquired. All functions called within end_request() _must_be_ atomic.