linux-kernel - Re: [PATCH 1/1] ext4: fix crash on BUG_ON in ext4_alloc_group

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Message-ID: <9aa773bd-44e8-4e4b-9628-dfbd3bd0a2af@huawei.com>
Date: Thu, 26 Sep 2024 22:35:03 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
CC: Jan Kara <jack@...e.cz>, <tytso@....edu>, <stable@...r.kernel.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>, Stéphane Graber
	<stgraber@...raber.org>, Christian Brauner <brauner@...nel.org>,
	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<linux-ext4@...r.kernel.org>, Wesley Hershberger
	<wesley.hershberger@...onical.com>, Yang Erkun <yangerkun@...wei.com>
Subject: Re: [PATCH 1/1] ext4: fix crash on BUG_ON in ext4_alloc_group_tables

On 2024/9/26 22:19, Aleksandr Mikhalitsyn wrote:
> On Thu, Sep 26, 2024 at 3:58 PM Baokun Li <libaokun1@...wei.com> 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@...ntu:/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