linux-ext4 - e2fsck -D lead to severely damaged filesystem

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Date:   Mon, 15 Jan 2018 08:23:29 +0100
From:   Nikola Ciprich <nikola.ciprich@...uxbox.cz>
To:     linux-ext4@...r.kernel.org
Cc:     nik@...uxbox.cz
Subject: e2fsck -D lead to severely damaged filesystem

Hello dear ext4 developers,

I'd like to ask about following problem I hit yesterday
(and which I'm a bit responsible for, I guess).

we were dealing with slow access to directories with lots of
files (large maildirs), so after some  tests, I came to conclusion
that optimizing directories using e2fsck -D (on unmounted FS of course)
helps a lot. So after testing this on our test box, I did it on production
mailserver mail volume. The I decided to do some tests on newer kernel,
so I rebooted test box and got lots of fs errors..

I checked production box, and it got bad as well:

lots  of dx_probe:829: inode #15949784: block 35579: comm deliver: Directory hole found
messages.. 

so I unmounted fs again, run fsck, and got zillion of:

Inode 18378187 ref count is 2, should be 1.  Fix? yes

Unattached inode 18378194
Connect to /lost+found? yes

messages.. 

after ~3 hours, I gave up, and recovered FS from backup.. checking fs after
"repair" showed that some of large mailboxes vanished completely (and appeared in lost+found)

I think I can rule out hardware problem, since it appeared on two completely different
systems after some action.. but I'll try to prepare new test environment and reproduce it.

What I think might be my big mistake is that I was using quite old e2fsprogs - 1.42.6,
kernel was 4.4.52 (which I know is also a bit old, we're already testig 4.14.x)

My question is, was that  some known e2fsck problem which got fixed in new version?

Or did I do something wrong?

I'm going to retry using 1.43.8, but still I'd be a bit calmer to know it was known problem
and got fixed :)

If I could provide some more information, please let me know..

BR

nik

PS: both systems were running latest centos 6 (but with newer kernel and e2fsprogs)

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