ext4: convert write_begin methods to stable_page_writes semantics

Use wait_for_stable_page() instead of wait_on_page_writeback()
Signed-off-by: NDmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: NJan Kara <jack@suse.cz>

fs/ext4/inode.c

@@ -969,7 +969,8 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
 		ext4_journal_stop(handle);
 		goto retry_grab;
 	}
-	wait_on_page_writeback(page);
+	/* In case writeback began while the page was unlocked */
+	wait_for_stable_page(page);
 
 	if (ext4_should_dioread_nolock(inode))
 		ret = __block_write_begin(page, pos, len, ext4_get_block_write);
@@ -2678,7 +2679,7 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
 		goto retry_grab;
 	}
 	/* In case writeback began while the page was unlocked */
-	wait_on_page_writeback(page);
+	wait_for_stable_page(page);
 
 	ret = __block_write_begin(page, pos, len, ext4_da_get_block_prep);
 	if (ret < 0) {