[Samba] Samba 3.5.7-3.5.1-2573 not able to shutdown old processes which results in locked files

[Marcus Mundt]

Dear Samba users,

Samba tries to close old connections on a new session setup from the same machine, but fails. Those connections result in locked files which the users can't access - i.e. save or open. I have to kill them via "kill -9 pid". 

smb.conf:
http://pastebin.com/bYRFJwu0

smb.inc:
http://pastebin.com/JV9KyDyA

Using "reset on zero vc = yes" seems to reduce the symptoms but does not solve the issues. Since Samba does not seem to be able to close (all) connections. See logs below.

Abstracts of the logs:
/var/log/samba/__ffff_X.X.X.X.log: 
switch message SMBsesssetupX (pid 14730) conn 0x0
shutdown_other_smbds: shutting down pid 14730 (IP ::ffff:X.X.X.X)

Then I do a manual shutdown via kill -9:
/var/log/samba/smbd.log:
[2016/12/16 11:17:38.849553,  3] smbd/server.c:259(remove_child_pid)
  smbd/server.c:259 Unclean shutdown of pid 14730
[2016/12/16 11:17:38.849606,  1] smbd/server.c:267(remove_child_pid)
  Scheduled cleanup of brl and lock database after unclean shutdown
[2016/12/16 11:17:58.869695,  1] smbd/server.c:240(cleanup_timeout_fn)
  Cleaning up brl and lock database after unclean shutdown
[2016/12/16 11:17:58.870256,  2] lib/messages_local.c:289(message_notify)
  message to process 14730 failed - No such process
[2016/12/16 11:17:58.870290,  2] lib/messages_local.c:379(messaging_tdb_send)
  pid 14730 doesn't exist - deleting messages record
[2016/12/16 11:17:58.870311,  2] lib/messages.c:127(traverse_fn)
  pid 14730 doesn't exist - deleting connections -1 []

This happens with ASCII files and M$ Office files. When users are editing a file and saving the file fails, they lose some hours of work. Any hints highly appreciated. I'm now thinking of trying out "SO_KEEPALIVE".
Very similar issues with Samba 3.6.6 on another Samba Server in our company.

Thanks for your support! Cheers,
Marcus