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

[Baokun Li]

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