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Date:   Fri, 16 Dec 2022 08:10:09 -0500
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     Jun Nie <jun.nie@linaro.org>
Cc:     stable@vger.kernel.org, djwong@kernel.org, jack@suse.cz,
        jlayton@kernel.org, lczerner@redhat.com,
        linux-ext4@vger.kernel.org, xuyang2018.jy@fujitsu.com
Subject: Re: [PATCH v1] ext4: Remove deprecated noacl/nouser_xattr options
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References: <166431556706.3511882.843791619431401636.b4-ty@mit.edu>
 <20221216034116.869864-1-jun.nie@linaro.org>
 <Y5wGZG05uicAPscI@mit.edu>
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Here is a proper, minmized reproducer which reproduces on upstream, for someone
who wants to try to work this bug.

On Fri, Dec 16, 2022 at 12:47:16AM -0500, Theodore Ts'o wrote:
> Fixing this the clean and proper way, which is by making
> ext4_xattr_move_to_block() more intelligent/efficient, is left as an
> exercise to the reader.

For someone who wants to work the bug, here is a cleaner, properly
minimzed, easier-for-humans-to-understand reproducer:

#!/bin/bash -vx
#
# This reproduces an ext4 bug caused by an unfortunate interaction
# between lazytime updates happening when a file system is being
# unmounted and expand_extra_isize
#
# Initially discovered via syzkaller:
# https://syzkaller.appspot.com/bug?id=3613786cb88c93aa1c6a279b1df6a7b201347d08
#

img=/tmp/foo.img
dir=/mnt
file=$dir/file0

rm -f $img
mke2fs -Fq -t ext4 -I 256 -O ea_inode -b 1024 $img 200k
mount $img $dir
v=$(dd if=/dev/zero bs=2000 count=1 2>/dev/null | tr '\0' =)
touch $file
attr -q -s test -V $v $file
umount $dir
mount -o debug_want_extra_isize=128,lazytime /tmp/foo.img $dir
cat $file
umount $dir