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From: Luis Henriques <luis.henriques@linux.dev>
To: Ben Hutchings <ben@decadent.org.uk>
Cc: linux-ext4@vger.kernel.org,  =?utf-8?Q?Herv=C3=A9?= Werner
 <dud225@hotmail.com>,
  Diederik de Haas <didi.debian@cknow.org>,  1039883@bugs.debian.org,
  Salvatore Bonaccorso <carnil@debian.org>, harshad shirwadkar
 <harshadshirwadkar@gmail.com>
Subject: Re: linux: ext4 corruption with symlinks
In-Reply-To: <e6797603353b8162df6c29777ed5936af4d11b32.camel@decadent.org.uk>
	(Ben Hutchings's message of "Mon, 10 Jun 2024 18:03:58 +0200")
References: <168802788716.2369531.1979971093539266086.reportbug@ariane.home>
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	<e6797603353b8162df6c29777ed5936af4d11b32.camel@decadent.org.uk>
Date: Fri, 14 Jun 2024 17:18:45 +0100
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On Mon 10 Jun 2024 06:03:58 PM +02, Ben Hutchings wrote;

> On Sun, 5 Nov 2023 16:12:41 +0000 Herv=C3=A9 Werner <dud225@hotmail.com>
> wrote:
>> Hello
>>=20
>> I'm sorry for the delay.
>>=20
>> > 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:
>>=C2=A0=C2=A0 sudo mkfs -t ext4 -O fast_commit,inline_data /dev/sdb
>>=C2=A0=C2=A0 sudo mount /dev/sdb /mnt/
>>=C2=A0=C2=A0 sudo install -d -o myuser /mnt/annex
>>=C2=A0=C2=A0 cd /mnt/annex
>>=C2=A0=C2=A0 git init && git annex init
>>=C2=A0=C2=A0 for i in {1..2}; do
>>=C2=A0=C2=A0=C2=A0=C2=A0 for i in {1..10000}; do
>>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 dd if=3D/dev/urandom of=3Dfile-${i} =
bs=3D1K count=3D1 2>/dev/null
>>=C2=A0=C2=A0=C2=A0=C2=A0 done
>>=C2=A0=C2=A0=C2=A0=C2=A0 git annex add -J cpus . >/dev/null && git annex =
sync -J cpus && git annex fsck -J cpus >/dev/null
>>=C2=A0=C2=A0=C2=A0=C2=A0 git rm * && git annex sync=C2=A0 && git annex dr=
opunused all
>>=C2=A0=C2=A0 done
>>=20
>> Then at some point the following error appears:
>>=C2=A0=C2=A0 EXT4-fs error (device sdb): ext4_map_blocks:577: inode #3942=
343: 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@bytedance.com>
> Date:   Thu Dec 23 11:23:37 2021 +0800
>=20=20
>     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.

Because I recently fixed an issue in the fast commit code[1] I was hoping
that you were hitting the same bug.  I've executed the reproducer with the
fix (which hasn't been merged yet) and realised it's definitely a
different problem.

Debugged the issue a bit, it seems to be related with the fact that
ext4_fc_write_inode_data() isn't able to cope with the fact that
'ei->i_fc_lblk_len' is set to EXT_MAX_BLOCKS.

I'm CC'ing Harshad, maybe he has some idea.

[1] https://lore.kernel.org/all/20240529092030.9557-2-luis.henriques@linux.=
dev

Cheers,
--=20
Lu=C3=ADs