[Samba] Error timeout mutex.tdb with samba 3nt migration to samba 4

[Trenta sis]

Hi,

I'm trying to migrate samba nt 3 doamin to samba 4 AD, I have migrated and
seems to works and recover users, but after some time I have received some
error and now I can't add machien to domain, add permission to folders from
doamin user, only error detected is

# cat /usr/local/samba/var/log.winbindd-idmap
[2016/06/09 12:06:53.547280,  0]
../source3/lib/util_tdb.c:494(tdb_chainlock_with_timeout_internal)
  tdb_chainlock_with_timeout_internal: alarm (40) timed out for key
dc.domain.com in tdb /usr/local/samba/var/lock/mutex.tdb
[2016/06/09 12:06:53.547469,  0]
../source3/winbindd/winbindd_cm.c:1032(cm_prepare_connection)
  cm_prepare_connection: mutex grab failed for dc.domain.com
[2016/06/09 12:07:33.578631,  0]
../source3/lib/util_tdb.c:494(tdb_chainlock_with_timeout_internal)
  tdb_chainlock_with_timeout_internal: alarm (40) timed out for key
dc.domain.com in tdb /usr/local/samba/var/lock/mutex.tdb
[2016/06/09 12:07:33.578896,  0]
../source3/winbindd/winbindd_cm.c:1032(cm_prepare_connection)
  cm_prepare_connection: mutex grab failed for dc.domain.com
[2016/06/09 12:09:48.079144,  0]
../source3/lib/util_tdb.c:494(tdb_chainlock_with_timeout_internal)
  tdb_chainlock_with_timeout_internal: alarm (40) timed out for key
dc.domain.com in tdb /usr/local/samba/var/lock/mutex.tdb
[2016/06/09 12:09:48.079316,  0]
../source3/winbindd/winbindd_cm.c:1032(cm_prepare_connection)
  cm_prepare_connection: mutex grab failed for dc.domain.com


mutex.tdb has a minimal size but with an old date (two days ago), Other tdb
files are modified in last minutes

Where could be the problem? What is mutex.tdb?

Thanks