Btrfs: correctly flush compressed data before/after direct IO

For compressed writes, after doing the first filemap_fdatawrite_range() we
don't get the pages tagged for writeback immediately. Instead we create
a workqueue task, which is run by other kthread, and keep the pages locked.
That other kthread compresses data, creates the respective ordered extent/s,
tags the pages for writeback and unlocks them. Therefore we need a second
call to filemap_fdatawrite_range() if we have compressed writes, as this
second call will wait for the pages to become unlocked, then see they became
tagged for writeback and finally wait for the writeback to finish.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/file.c

@@ -1692,8 +1692,18 @@ static ssize_t __btrfs_direct_write(struct kiocb *iocb,
 		err = written_buffered;
 		goto out;
 	}
+	/*
+	 * Ensure all data is persisted. We want the next direct IO read to be
+	 * able to read what was just written.
+	 */
 	endbyte = pos + written_buffered - 1;
-	err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
+	err = filemap_fdatawrite_range(file->f_mapping, pos, endbyte);
+	if (!err && test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
+			     &BTRFS_I(file_inode(file))->runtime_flags))
+		err = filemap_fdatawrite_range(file->f_mapping, pos, endbyte);
+	if (err)
+		goto out;
+	err = filemap_fdatawait_range(file->f_mapping, pos, endbyte);
 	if (err)
 		goto out;
 	written += written_buffered;

fs/btrfs/inode.c

@@ -7015,7 +7015,17 @@ static int lock_extent_direct(struct inode *inode, u64 lockstart, u64 lockend,
 			btrfs_put_ordered_extent(ordered);
 		} else {
 			/* Screw you mmap */
-			ret = filemap_write_and_wait_range(inode->i_mapping,
+			ret = filemap_fdatawrite_range(inode->i_mapping,
+						       lockstart,
+						       lockend);
+			if (!ret && test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
+					     &BTRFS_I(inode)->runtime_flags))
+				ret = filemap_fdatawrite_range(inode->i_mapping,
+							       lockstart,
+							       lockend);
+			if (ret)
+				break;
+			ret = filemap_fdatawait_range(inode->i_mapping,
 						      lockstart,
 						      lockend);
 			if (ret)