cramfs: read_mapping_page() is synchronous

Since commit 67f9fd91, the code to wait for the read to complete has
been dead.  That commit wrongly stated that the read was synchronous
already; this seems to have been a confusion about which ->readpage
operation was being called.  Instead of reintroducing an asynchronous
version of read_mapping_page(), call the readahead code directly to
submit all reads first before waiting for them in read_mapping_page().
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

fs/cramfs/inode.c

@@ -183,6 +183,7 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
 				unsigned int len)
 {
 	struct address_space *mapping = sb->s_bdev->bd_inode->i_mapping;
+	struct file_ra_state ra;
 	struct page *pages[BLKS_PER_BUF];
 	unsigned i, blocknr, buffer;
 	unsigned long devsize;
@@ -212,6 +213,9 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
 	devsize = bdev_nr_bytes(sb->s_bdev) >> PAGE_SHIFT;
 
 	/* Ok, read in BLKS_PER_BUF pages completely first. */
+	file_ra_state_init(&ra, mapping);
+	page_cache_sync_readahead(mapping, &ra, NULL, blocknr, BLKS_PER_BUF);
+
 	for (i = 0; i < BLKS_PER_BUF; i++) {
 		struct page *page = NULL;
 
@@ -224,19 +228,6 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
 		pages[i] = page;
 	}
 
-	for (i = 0; i < BLKS_PER_BUF; i++) {
-		struct page *page = pages[i];
-
-		if (page) {
-			wait_on_page_locked(page);
-			if (!PageUptodate(page)) {
-				/* asynchronous error */
-				put_page(page);
-				pages[i] = NULL;
-			}
-		}
-	}
-
 	buffer = next_buffer;
 	next_buffer = NEXT_BUFFER(buffer);
 	buffer_blocknr[buffer] = blocknr;