linux-ext4 - Re: linux: ext4 corruption with symlinks

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Message-ID: <e6797603353b8162df6c29777ed5936af4d11b32.camel@decadent.org.uk>
Date: Mon, 10 Jun 2024 18:03:58 +0200
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-ext4@...r.kernel.org, Hervé Werner
	 <dud225@...mail.com>
Cc: Diederik de Haas <didi.debian@...ow.org>, 1039883@...s.debian.org, 
	Salvatore Bonaccorso
	 <carnil@...ian.org>
Subject: Re: linux: ext4 corruption with symlinks

On Sun, 5 Nov 2023 16:12:41 +0000 Hervé Werner <dud225@...mail.com>
wrote:
> Hello
> 
> I'm sorry for the delay.
> 
> > Are you able to reliably preoeduce the issue and can bisect it to
> > the introducing commit?
> I faced this issue on real data but I struggled to find a reliable
> scenario to reproduce it. Here is what I just came up with:
>   sudo mkfs -t ext4 -O fast_commit,inline_data /dev/sdb
>   sudo mount /dev/sdb /mnt/
>   sudo install -d -o myuser /mnt/annex
>   cd /mnt/annex
>   git init && git annex init
>   for i in {1..2}; do
>     for i in {1..10000}; do
>       dd if=/dev/urandom of=file-${i} bs=1K count=1 2>/dev/null
>     done
>     git annex add -J cpus . >/dev/null && git annex sync -J cpus && git annex fsck -J cpus >/dev/null
>     git rm * && git annex sync  && git annex dropunused all
>   done
> 
> Then at some point the following error appears:
>   EXT4-fs error (device sdb): ext4_map_blocks:577: inode #3942343: block 4: comm git-annex:w: lblock 1 mapped to illegal pblock 4 (length 1)
[...]

I can also reproduce this error message using the above script and:

- Linux 6.10-rc2
- A 2 GiB loopback devic instead of /dev/sdb

I bisected this back to:

commit 9725958bb75cdfa10f2ec11526fdb23e7485e8e4
Author: Xin Yin <yinxin.x@...edance.com>
Date:   Thu Dec 23 11:23:37 2021 +0800
 
    ext4: fast commit may miss tracking unwritten range during ftruncate

It is still possible to cleanly revert that commit from 6.10-rc2, and
doing so removes the error message.

Ben.

-- 
Ben Hutchings
Reality is just a crutch for people who can't handle science fiction.


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