[PATCH] Avoid CTDB daemon deadlock while reading db sequence number (bug 13021)

[Martin Schwenke]

On Mon, 11 Sep 2017 13:59:02 +1000, Amitay Isaacs via samba-technical
<samba-technical at lists.samba.org> wrote:

> Once the recovery starts and databases are frozen, then all the record
> access is postponed till the recovery is complete except reading the
> database sequence number.  Database access for reading sequence number
> is done via a control which does not check if the databases are frozen
> or not.
> 
> If the database is frozen and if the freeze transaction is not started
> (this can happen when a node is inactive, or during recovery when the
> database is frozen but the transaction has not yet started), then trying
> to read sequence number will cause ctdb daemon to deadlock.
> 
> Before reading the sequence number, check if the database access is
> allowed.
> 
> Please review and push.

Reviewed-by: Martin Schwenke <martin at meltin.net>

Mega-push coming...  :-)

peace & happiness,
martin