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Date:   Tue, 19 May 2020 11:29:17 +0800
From:   JeffleXu <>
To:     Eric Whitney <>
Subject: Re: [PATCH RFC] ext4: fix partial cluster initialization when
 splitting extent

On 5/19/20 6:08 AM, Eric Whitney wrote:
> Hi, Jeffle:
> What kernel were you running when you observed your failures?  Does your
> patch resolve all observed failures, or do any remain?  Do you have a
> simple test script that reproduces the bug?
> I've made almost 1000 runs of shared/298 on various bigalloc configurations
> using Ted's test appliance on 5.7-rc5 and have not observed a failure.
> Several auto group runs have also passed without failures.  Ideally, I'd
> like to be able to reproduce your failure to be sure we fully understand
> what's going on.  It's still the case that the "2" is wrong, but I think
> that code in rm_leaf may be involved in an unexpected way.
> Thanks,
> Eric

Hi Eric,

Following on is my test environment.

kernel: 5.7-rc4-git-eb24fdd8e6f5c6bb95129748a1801c6476492aba

e2fsprog: latest release version 1.45.6 (20-Mar-2020)

xfstests: git://, master 
branch, latest commit

1. Test device

I run the test in a VM and the VM is setup by qemu. The size of vdb is 1G,



vdb    254:16   0   1G  0 disk


and is initialized by:


qemu-img create -f qcow2 /XX/disk1.qcow2 1G

qemu-kvm -drive file=/XX/disk1.qcow2,if=virtio,format=qcow2 ...


2. Test script

local.config of xfstests is like:

export TEST_DEV=/dev/vdb
export TEST_DIR=/mnt/test
export SCRATCH_DEV=/dev/vdc
export SCRATCH_MNT=/mnt/scratch

Following on is an example script to reproduce the failure:



for i in `seq 100`; do
         echo y | mkfs.ext4 -O bigalloc -C 16K /dev/vdb

         ./check shared/298

         if [[ $status == 1 ]]; then
                 echo "$i exit"


Indeed the failure occurs occasionally. Sometimes the script stops at 
iteration 4, or sometimes

at iteration 2, 7, 24.

The failure occurs with the following dmesg report:


[  387.471876] EXT4-fs error (device vdb): mb_free_blocks:1457: group 1, 
block 158084:freeing already freed block (bit 6753); block bitmap corrupt.
[  387.473729] EXT4-fs error (device vdb): ext4_mb_generate_buddy:747: 
group 1, block bitmap and bg descriptor inconsistent: 19550 vs 19551 
free clusters


3. About the applied patch

The applied patch does fix the failure in my test environment. At least 
the failure doesn't occur after running the full 100 iterations.



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