linux-kernel - Regression: squashfs issues since change "squashfs: migrate from ll_rw

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Date:   Tue, 14 Jul 2020 21:41:07 +0200
From:   Bernd Amend <bernd.amend@...il.com>
To:     phillip@...ashfs.org.uk, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Bernd Amend <bernd.amend@...il.com>,
        Stefan Rommel <stefanrommel@...il.com>
Subject: Regression: squashfs issues since change "squashfs: migrate from
 ll_rw_block usage to BIO"

Hi,

With the Linux Kernel version 5.8-rc5/master I am unable to mount some
squashfs filesystems compressed with "-comp lz4".
If I try to mount them I get the following error:
[    1.084246] SQUASHFS error: lz4 decompression failed, data probably corrupt
[    1.084545] SQUASHFS error: Failed to read block 0x873e1001: -5
[    1.084761] SQUASHFS error: Unable to read metadata cache entry [873e0fff]
[    1.084983] SQUASHFS error: Unable to read directory block [873e0fff:1586]
[    1.122564] SQUASHFS error: Unable to read metadata cache entry [873e0fff]
[    1.122708] SQUASHFS error: Unable to read directory block [873e0fff:1586]
[    1.122862] Starting init: /sbin/init exists but couldn't execute
it (error -5)
[    1.123027] SQUASHFS error: Unable to read metadata cache entry [873e0fff]
[    1.123152] SQUASHFS error: Unable to read directory block [873e0fff:1586]
[    1.123279] Starting init: /etc/init exists but couldn't execute it
(error -5)
[    1.123444] SQUASHFS error: Unable to read metadata cache entry [873e0fff]
[    1.123573] SQUASHFS error: Unable to read directory block [873e0fff:1586]
[    1.123713] Starting init: /bin/init exists but couldn't execute it
(error -5)
[    1.123900] SQUASHFS error: Unable to read metadata cache entry [873e0fff]

or

[ 4960.910693] attempt to access beyond end of device
[ 4960.910695] loop0: rw=2048, want=46, limit=40
[ 4960.910696] SQUASHFS error: Failed to read block 0x4001: -5
[ 4960.910697] SQUASHFS error: Unable to read metadata cache entry [3fff]
[ 4960.910698] SQUASHFS error: Unable to read inode 0x20c5000c

I bisected the issue to the commit "squashfs: migrate from ll_rw_block
usage to BIO"
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/fs/squashfs?id=93e72b3c612adcaca13d874fcc86c53e6c8da541

The issue can be reproduced by downloading
https://theworldsend.eu/demo.squashfs (20K) and the following command
line.
# mount demo.squashfs mnt && ls mnt && umount mnt

The same squashfs can be mounted using Linux <=5.7.8.
The kernel config is identical to the Arch Linux Kernel configuration,
build using gcc 9 and 10 on x86_64.

Best regards,
Bernd Amend