zonefs: Do not propagate iomap_dio_rw() ENOTBLK error to user space

The call to invalidate_inode_pages2_range() in __iomap_dio_rw() may
fail, in which case -ENOTBLK is returned and this error code is
propagated back to user space trhough iomap_dio_rw() ->
zonefs_file_dio_write() return chain. This error code is fairly obscure
and may confuse the user. Avoid this and be consistent with the behavior
of zonefs_file_dio_append() for similar invalidate_inode_pages2_range()
errors by returning -EBUSY to user space when iomap_dio_rw() returns
-ENOTBLK.
Suggested-by: Christoph Hellwig <hch@infradead.org>
Fixes: 8dcc1a9d ("fs: New zonefs file system")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Tested-by: Hans Holmberg <hans.holmberg@wdc.com>

fs/zonefs/file.c

@@ -581,11 +581,21 @@ static ssize_t zonefs_file_dio_write(struct kiocb *iocb, struct iov_iter *from)
 		append = sync;
 	}
 
-	if (append)
+	if (append) {
 		ret = zonefs_file_dio_append(iocb, from);
-	else
+	} else {
+		/*
+		 * iomap_dio_rw() may return ENOTBLK if there was an issue with
+		 * page invalidation. Overwrite that error code with EBUSY to
+		 * be consistent with zonefs_file_dio_append() return value for
+		 * similar issues.
+		 */
 		ret = iomap_dio_rw(iocb, from, &zonefs_write_iomap_ops,
 				   &zonefs_write_dio_ops, 0, NULL, 0);
+		if (ret == -ENOTBLK)
+			ret = -EBUSY;
+	}
+
 	if (zonefs_zone_is_seq(z) &&
 	    (ret > 0 || ret == -EIOCBQUEUED)) {
 		if (ret > 0)