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Message-ID: <941f8157-6515-40d3-98bd-ca1c659ef9e0@huawei.com> Date: Thu, 26 Sep 2024 21:58:24 +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 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: 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
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