krb5-18.2: MDB_BAD_RSLOT: Invalid reuse of reader locktable slot

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krb5-18.2: MDB_BAD_RSLOT: Invalid reuse of reader locktable slot

rachit chokshi
Hello,
I was trying out the latest release hoping to reap the benefits of LMDB for
our systems. However each time I start krb5kdc and kadmin processes
separately (one after another/at a different point in time) I see below in
krb5kdc logs.

*LMDB read failure (path: /var/kerberos/krb5kdc/principal.mdb):
MDB_BAD_RSLOT: Invalid reuse of reader locktable slot*

This problem goes away when i restart both services at the same time by
doing "*systemctl restart kadmin krb5kdc*". However if any of them is
individually restarted later, the above error starts showing up again.

i can post my conf files but this is a vanilla setup with only the "
*[dbmodules]"* section added to *kdc.conf*, rest all is default. The distro
I am using is fedora rawhide.

If anybody has seen this, pointers in the correct direction are greatly
appreciated. TIA :)

Regards,
Rachit
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Re: krb5-18.2: MDB_BAD_RSLOT: Invalid reuse of reader locktable slot

Greg Hudson
On 6/18/20 4:53 AM, rachit chokshi wrote:
> *LMDB read failure (path: /var/kerberos/krb5kdc/principal.mdb):
> MDB_BAD_RSLOT: Invalid reuse of reader locktable slot*

After some off-list debugging, I determined that the LMDB reader table
entries for krb5kdc and kadmind appear as stale to other processes and
can be reclaimed, because both daemons open the DB before daemonizing.

I have filed a ticket and a pull request:

https://krbdev.mit.edu/rt/Ticket/Display.html?id=8918
https://github.com/krb5/krb5/pull/1088
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