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

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Message-ID: <CAEivzxcR+yy1HcZSXmRKOuAuGDnwr=EK_G5mRgk4oNxEPMH_=A@mail.gmail.com>
Date: Thu, 26 Sep 2024 16:19:39 +0200
From: Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To: Baokun Li <libaokun1@...wei.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 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
Segmentation fault

My kernel's commit hash is 684a64bf32b6e488004e0ad7f0d7e922798f65b6

Maybe it somehow depends on the resize2fs version?

Kind regards,
Alex

>
> o_group = flexbg_size * 2 * n;
> o_size = (o_group + 1) * group_size;
> n_group: [o_group + flexbg_size, o_group + flexbg_size * 2)
>
> Take n=1,flexbg_size=16 as an example:
>                                                   last:47
> |----------------|----------------|o---------------|--------------n-|
>                                    old:32 >>>           new:62
>
> Thus the replicator can be simplified as:
>
> img=test.img
> truncate -s 600M $img
> mkfs.ext4 -F $img -b 1024 -G 16 264M
> dev=`losetup -f --show $img`
> mkdir -p /tmp/test
> mount $dev /tmp/test
> resize2fs $dev 504M
>
>
> --
> Cheers,
> Baokun
>