Re: [PATCH 1/1] ext4: fix crash on BUG_ON in ext4_alloc_group_tables

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On 2024/9/26 22:19, Aleksandr Mikhalitsyn wrote:
On Thu, Sep 26, 2024 at 3:58 PM Baokun Li <libaokun1@xxxxxxxxxx> wrote:
On 2024/9/26 19:32, Aleksandr Mikhalitsyn wrote:
Question to you and Jan. Do you guys think that it makes sense to try
to create a minimal reproducer for this problem without Incus/LXD involved?
(only e2fsprogs, lvm tools, etc)

I guess this test can be put in the xfstests test suite, right?

Kind regards,
Alex
I think it makes sense, and it's good to have more use cases to look
around some corners. If you have an idea, let it go.
Minimal reproducer:

mkdir -p /tmp/ext4_crash/mnt
EXT4_CRASH_IMG="/tmp/ext4_crash/disk.img"
rm -f $EXT4_CRASH_IMG
truncate $EXT4_CRASH_IMG --size 25MiB
EXT4_CRASH_DEV=$(losetup --find --nooverlap --direct-io=on --show
$EXT4_CRASH_IMG)
mkfs.ext4 -E nodiscard,lazy_itable_init=0,lazy_journal_init=0 $EXT4_CRASH_DEV
mount $EXT4_CRASH_DEV /tmp/ext4_crash/mnt
truncate $EXT4_CRASH_IMG --size 3GiB
losetup -c $EXT4_CRASH_DEV
resize2fs $EXT4_CRASH_DEV

Hi Alex,

This replicator didn't replicate the issue in my VM, so I took a deeper
look. The reproduction of the problem requires the following:
That's weird. Have just tried once again and it reproduces the issue:

root@ubuntu:/home/ubuntu# mkdir -p /tmp/ext4_crash/mnt
EXT4_CRASH_IMG="/tmp/ext4_crash/disk.img"
rm -f $EXT4_CRASH_IMG
truncate $EXT4_CRASH_IMG --size 25MiB
EXT4_CRASH_DEV=$(losetup --find --nooverlap --direct-io=on --show
$EXT4_CRASH_IMG)
mkfs.ext4 -E nodiscard,lazy_itable_init=0,lazy_journal_init=0 $EXT4_CRASH_DEV
mount $EXT4_CRASH_DEV /tmp/ext4_crash/mnt
truncate $EXT4_CRASH_IMG --size 3GiB
losetup -c $EXT4_CRASH_DEV
resize2fs $EXT4_CRASH_DEV
mke2fs 1.47.0 (5-Feb-2023)
Creating filesystem with 6400 4k blocks and 6400 inodes

Allocating group tables: done
Writing inode tables: done
Creating journal (1024 blocks): done
Writing superblocks and filesystem accounting information: done

resize2fs 1.47.0 (5-Feb-2023)
Filesystem at /dev/loop4 is mounted on /tmp/ext4_crash/mnt; on-line
resizing required
old_desc_blocks = 1, new_desc_blocks = 1
I can see why, on my side I mkfsed a 25M sized disk, and the ext4
block size is 1024 by default, whereas on your side it's 4096.
I set the block size to 4096 and it also reproduced the issue.

Thanks for your feedback!


Cheers,
Baokun





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