From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxim Malkov Subject: Online resizing of filesystem mounted with backup superblock causes corruption Date: Wed, 24 Dec 2014 01:32:42 +0300 Message-ID: <5499ED8A.5010907@ispras.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Andrey Tsyvarev , Alexey Khoroshilov To: linux-ext4@vger.kernel.org Return-path: Received: from mail.ispras.ru ([83.149.199.45]:45190 "EHLO mail.ispras.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751499AbaLWWcq (ORCPT ); Tue, 23 Dec 2014 17:32:46 -0500 Sender: linux-ext4-owner@vger.kernel.org List-ID: # mkfs.ext4 /dev/loop0 100M # adjust if necessary, should be less than partition size Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729 (pick one) # mount -t ext4 -o sb=40961 /dev/loop0 /media/ # resize2fs /dev/loop0 resize2fs 1.42.12 (29-Aug-2014) Filesystem at /dev/loop0 is mounted on /media; on-line resizing required old_desc_blocks = 1, new_desc_blocks = 4 Now, depending on your luck, various things may happen. resize2fs may hang. You might see BUG() in your dmesg. Either way, system will become severely corrupted (as indicated by fsck). You won't be able to mount it, either. [ 2669.510800] EXT4-fs (loop0): resizing filesystem from 128000 to 256000 blocks [ 2669.513558] EXT4-fs warning (device loop0): reserve_backup_gdb:969: reserved block 32770 not at offset 1 [ 2669.513569] EXT4-fs (loop0): resized filesystem to 256000 [ 2669.516328] EXT4-fs warning (device loop0): ext4_group_extend:1734: can't shrink FS - resize aborted -- Maxim Malkov Software Engineering Department, ISPRAS