On Sat 10/Jan/2015 00:08:04 +0100 Sam Varshavchik wrote:
> Alessandro Vesely writes:
>
>>> Currently, the shutdown code just gives up, after a timeout, in this
>>> manner. I
>>> do agree that an attempt should be made to kill all processes, after a
>>> reasonable timeout, so it's something that I need to look at.
>>
>> To kill by pid is going to be difficult for forked filters. I issue a call
>> kill(0, SIGTERM) when the pipe is closed, but I had previously called
>> setsid().
>> SIGTERM (15) should suffice to quickly exit; SIGKILL (9) is what I'd call
>> "overkill". It seems several users issue `killall -9 ...`. It shouldn't be
>> needed, and I'd expect some kind of bug report if runaway children refuse to
>> exit, please.
>
> Well, there are various ways to make sure that child processes get SIGKILLed.
> The traditional way to do this is with process groups.
Err... I call setsid() because it's what the daemon() function usually does,
albeit filters run by courierfilter don't fork. Probably, setpgid() or
setpgrp() are better choices. (Let me recall that a session consists of one or
more program groups.)
> Probably the best thing to do would be to kill all the processes, but exit
> with
> a non-zero exit code.
You're talking about courierfilter behavior, right? Filters should kill all of
their child processes or threads when fd0 is closed. However, if a filter
fails to do so, it deserves a SIGKILL. Logging filtername is probably useful.
If a filter forked children, it may be worth to attempt to kill them too. For
example, something like:
pid_t p = pp->p;
if (getpgid(p) != getpgid(getpid()))
p = -p;
kill(p, SIGKILL);
Alternatively, a new group can be created by courierfilter right after forking
each new filter. That way, the "if" above is always true unless a filter
maliciously sets its group id back to courierfilter's one.
> systemd takes this one step further, and puts all systemd-started processes in
> a container. On Fedora, a shutdown is going to kill any stuck filter
> processes,
> after filterctl stop bails out; so this is a non-issue on Fedora(*).
Hm... filterctl may be invoked by hand, no?
> (*) This is not intended to be an endorsement of systemd.
Thank goodness :-)
Ale
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