On winbind shutdown prior to the removal of gencache_stabilize we could crash due to races

[Richard Sharpe]

Hi folks,

We are seeing this on winbind shutdown:

--------------------------------------------------
2019-01-11 01:16:19 winbindd[17540]: [2019/01/11 01:16:19.153272,  0]
../source3/winbindd/winbindd.c:281(winbindd_sig_term_handler)
2019-01-11 01:16:19 systemd[1]: Starting Hammerspace Maintenance Target.
2019-01-11 01:16:19 winbindd[17540]:   Got sig[15] terminate (is_parent=0)
2019-01-11 01:16:19 winbindd[17497]: [2019/01/11 01:16:19.153546,  0]
../source3/winbindd/winbindd.c:281(winbindd_sig_term_handler)
2019-01-11 01:16:19 winbindd[17497]:   Got sig[15] terminate (is_parent=1)
2019-01-11 01:16:19 winbindd[17507]: [2019/01/11 01:16:19.153413,  0]
../source3/winbindd/winbindd.c:281(winbindd_sig_term_handler)
2019-01-11 01:16:19 winbindd[17507]:   Got sig[15] terminate (is_parent=0)
2019-01-11 01:16:19 systemd[1]: Stopped System Security Services Daemon.
2019-01-11 01:16:19 winbindd[17540]: [2019/01/11 01:16:19.162163,  0]
../lib/util/fault.c:78(fault_report)
2019-01-11 01:16:19 winbindd[17540]:
===============================================================
2019-01-11 01:16:19 winbindd[17540]: [2019/01/11 01:16:19.162202,  0]
../lib/util/fault.c:79(fault_report)
2019-01-11 01:16:19 winbindd[17540]:   INTERNAL ERROR: Signal 7 in pid
17540 (4.7.1-GIT-c0bd705-Hammerspace)
2019-01-11 01:16:19 winbindd[17540]:   Please read the
Trouble-Shooting section of the Samba HOWTO
2019-01-11 01:16:19 winbindd[17540]: [2019/01/11 01:16:19.162220,  0]
../lib/util/fault.c:81(fault_report)
2019-01-11 01:16:19 winbindd[17540]:
===============================================================
2019-01-11 01:16:19 winbindd[17540]: [2019/01/11 01:16:19.162232,  0]
../source3/lib/util.c:804(smb_panic_s3)
2019-01-11 01:16:19 winbindd[17540]:   PANIC (pid 17540): internal error
2019-01-11 01:16:19 winbindd[17540]: [2019/01/11 01:16:19.162550,  0]
../source3/lib/util.c:915(log_stack_trace)
2019-01-11 01:16:19 winbindd[17540]:   BACKTRACE: 25 stack frames:
--------------------------------------------------------------

This is with a 4.7.1ish version of Samba.

It seems to be due to a race between the parent and child with both of
them calling gencache_stabilize and with the right phase of the moon,
one seems to have closed the tdb (and thus unmapped the mutexes
memory) while the other is iterating the mutexes.

I see that the whole gencache_stabilize stuff was removed around December 2018.

1. Is it worth filing a bug in case the change needs back porting?

2. Would it be better in my case to remove the calls to
gencache_stabilize from winbind's shutdown or should I take the whole
change in 1386200be5c583c680c3894a11688a0e0a3d2285?

-- 
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)(传说杜康是酒的发明者)