URL:
https://github.com/SSSD/sssd/pull/107
Title: #107: WATCHDOG: Avoid non async-signal-safe from the signal_handler
simo5 commented:
"""
On Tue, 2016-12-13 at 05:59 -0800, Jakub Hrozek wrote:
On Tue, Dec 13, 2016 at 02:44:44AM -0800, Simo Sorce wrote:
> On Tue, 2016-12-13 at 02:25 -0800, fidencio wrote:
> > Pavel,
> >
> > On Tue, Dec 13, 2016 at 11:20 AM, Pavel Březina
<notifications(a)github.com>
> > wrote:
> >
> > > There are two scenarios:
> > >
> > > 1. timeshift during system boot -- it is very common to be several
> > > hours
> > > 2. timeshift due to an ntp update when booted up -- usually only few
> > > seconds, not a big deal
> > >
> > > The problem with tevent timer is that if we shift backwards the timer
> > > remains too far in the future. This applies to all timers, not only for
the
> > > watchdog. Forward shift is not a problem, it just executes the timers
> > > immediately. Resetting the watchdog helps in a way that sssd is not
killed,
> > > we don't have any capability to reschedule all timed event and we
actually
> > > can not tell that sssd will be functioning properly (dyndns, sudo
refresh,
> > > enumeration, domain refresh, even idle timer on socket activation)... all
> > > those operations that depends on time() would become unreliable.
> > >
> > > I think the best thing to do would be restart the process (although the
> > > question is how would this affect the boot up) and patch tevent to deal
> > > with timeshift either by using monotonic clock or by detecting them and
> > > altering timers accordingly.
> > >
> >
> > In the latest version of patch I've just called _exit(1) when the
timeshift
> > is detected.
> > About patching tevent, I've seen some old discussions happening and it
> > doesn't seem a trivial thing to do. Would the patch, as it is right now,
be
> > acceptable and then a work on tevent could be done later (yes, I'd add it
> > to my queue and do it as soon as we have an agreement on doing this)?
>
> This is really a blunt tool (calling exit()), but until tevent can be
> fixed the only other option would be to use some wrapper to keep track
> of all existing timed events and cancel and restart them all if the
> clock changes abruptly.
that's why I suggested signaling self to a tevent-driven signal handler
from where we can just set up the timer anew.
If there is any other way to 'break out' of the POSIX signal handler
into somewhere where we can call tevent/talloc (or in general unsafe
calls) I'm all ears.
I guess I need to understand better what exactly you want to do to be
able to advice on something. I can think of a coulpe of options, none of
them particularly elegant :)
Simo.
--
Simo Sorce * Red Hat, Inc * New York
"""
See the full comment at
https://github.com/SSSD/sssd/pull/107#issuecomment-266762324