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I noticed a clear regression with mdadm tests with this patch in 
md-next
(7e6ba434cc6080).

Before the patch, tests 07reshape5intr and 07revert-grow would fail
fairly infrequently (about 1 in 4 runs for the former and 1 in 30 runs
for the latter).

After this patch, both tests always fail.

I don't have time to dig into why this is, but it would be nice if
someone can at least fix the regression. It is hard to make any 
progress
on these tests if we are continuing to further break them.

I have tried with both ubuntu 22.04 kernel which is 5.15 and vanilla 
5.12, none of them
can pass your mentioned tests.

[root@localhost mdadm]# lsblk|grep vd
vda          252:0    0    1G  0 disk
vdb          252:16   0    1G  0 disk
vdc          252:32   0    1G  0 disk
vdd          252:48   0    1G  0 disk
[root@localhost mdadm]# ./test --dev=disk --disks=/dev/vd{a..d} 
--tests=05r1-add-internalbitmap
Testing on linux-5.12.0-default kernel
/root/mdadm/tests/05r1-add-internalbitmap... succeeded
[root@localhost mdadm]# ./test --dev=disk --disks=/dev/vd{a..d} 
--tests=07reshape5intr
Testing on linux-5.12.0-default kernel
/root/mdadm/tests/07reshape5intr... FAILED - see 
/var/tmp/07reshape5intr.log and /var/tmp/fail07reshape5intr.log for details
[root@localhost mdadm]# ./test --dev=disk --disks=/dev/vd{a..d} 
--tests=07revert-grow
Testing on linux-5.12.0-default kernel
/root/mdadm/tests/07revert-grow... FAILED - see 
/var/tmp/07revert-grow.log and /var/tmp/fail07revert-grow.log for details
[root@localhost mdadm]# head -10  /var/tmp/07revert-grow.log | grep mdadm
+ . /root/mdadm/tests/07revert-grow
*++ mdadm -CR --assume-clean /dev/md0 -l5 -n4 -x1 /dev/vda /dev/vdb 
/dev/vdc /dev/vdd /dev/vda /dev/vdb /dev/vdc /dev/vdd --metadata=0.9**
*
The above line is clearly wrong from my understanding.

And let's check ubuntu 22.04.

root@vm:/home/gjiang/mdadm# lsblk|grep vd
vda    252:0    0     1G  0 disk
vdb    252:16   0     1G  0 disk
vdc    252:32   0     1G  0 disk
root@vm:/home/gjiang/mdadm# ./test --dev=disk --disks=/dev/vd{a..d} 
--tests=05r1-failfast
Testing on linux-5.15.0-30-generic kernel
/home/gjiang/mdadm/tests/05r1-failfast... succeeded
root@vm:/home/gjiang/mdadm# ./test --dev=disk --disks=/dev/vd{a..c}   
--tests=07reshape5intr
Testing on linux-5.15.0-30-generic kernel
/home/gjiang/mdadm/tests/07reshape5intr... FAILED - see 
/var/tmp/07reshape5intr.log and /var/tmp/fail07reshape5intr.log for details
root@vm:/home/gjiang/mdadm# ./test --dev=disk --disks=/dev/vd{a..c} 
--tests=07revert-grow
Testing on linux-5.15.0-30-generic kernel
/home/gjiang/mdadm/tests/07revert-grow... FAILED - see 
/var/tmp/07revert-grow.log and /var/tmp/fail07revert-grow.log for details

So I would not consider it is regression.

[ ... ]

FYI: I've used loop devices on a virtio disk.

I later discovered Logans patches [1], which I were not aware of, as 
I'm not subscribed to the lists.

[1]: 
https://lore.kernel.org/linux-raid/20220519191311.17119-6-logang@deltatee.com/T/#u (local)

The series seems to acknowledge that there are open problems and tries 
to fix them.
So I've used his md-bug branch from 
https://github.com/sbates130272/linux-p2pmem but it didn't look better.

Thanks for your effort.

So I understand, the mdadm tests *are* supposed to work and every bug 
I see here is worth analyzing? Or is Logan hunting down everything 
anyway?

Yes, it was supposed to be. But unfortunately, it was kind of broken, 
good news is people are aware
of it and try to make it works/better, pls see other links.

[1] 
https://lore.kernel.org/linux-raid/EA6887B4-2A44-49D0-ACF9-C04CC92AFD87@oracle.com/T/#t (local)
[2] 
https://lore.kernel.org/linux-raid/CALTww2-mbfZRcHu_95Q+WANXZ9ayRwjXvyvqP5Gseeb86dEy=w@mail.gmail.com/T/#t (local)

Thanks,
Guoqing