direct I/O fallback sync simplification

In the case of direct I/O falling back to buffered I/O we sync data
twice currently: once at the end of generic_file_buffered_write using
filemap_write_and_wait_range and once a little later in
__generic_file_aio_write using do_sync_mapping_range with all flags set.

The wait before write of the do_sync_mapping_range call does not make
any sense, so just keep the filemap_write_and_wait_range call and move
it to the right spot.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

mm/filemap.c

@@ -2240,7 +2240,6 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
 		size_t count, ssize_t written)
 {
 	struct file *file = iocb->ki_filp;
-	struct address_space *mapping = file->f_mapping;
 	ssize_t status;
 	struct iov_iter i;
 
@@ -2252,15 +2251,6 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
 		*ppos = pos + status;
   	}
 	
-	/*
-	 * If we get here for O_DIRECT writes then we must have fallen through
-	 * to buffered writes (block instantiation inside i_size).  So we sync
-	 * the file data here, to try to honour O_DIRECT expectations.
-	 */
-	if (unlikely(file->f_flags & O_DIRECT) && written)
-		status = filemap_write_and_wait_range(mapping,
-					pos, pos + written - 1);
-
 	return written ? written : status;
 }
 EXPORT_SYMBOL(generic_file_buffered_write);
@@ -2359,10 +2349,7 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 		 * semantics.
 		 */
 		endbyte = pos + written_buffered - written - 1;
-		err = do_sync_mapping_range(file->f_mapping, pos, endbyte,
-					    SYNC_FILE_RANGE_WAIT_BEFORE|
-					    SYNC_FILE_RANGE_WRITE|
-					    SYNC_FILE_RANGE_WAIT_AFTER);
+		err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
 		if (err == 0) {
 			written = written_buffered;
 			invalidate_mapping_pages(mapping,