linux-kernel - Re: [tip:timers/urgent] Revert: Unify CLOCK_MONOTONIC and CLOCK

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Message-ID: <1937172.K7anUBJQAz@aspire.rjw.lan>
Date:   Thu, 26 Apr 2018 10:00:22 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Peter Anvin <hpa@...or.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Pavel Machek <pavel@....cz>, Kevin Easton <kevin@...rana.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        SergeySenozhatsky <sergey.senozhatsky@...il.com>,
        Jonathan Corbet <corbet@....net>,
        linux-tip-commits@...r.kernel.org, Mike Galbraith <efault@....de>
Subject: Re: [tip:timers/urgent] Revert: Unify CLOCK_MONOTONIC and CLOCK_BOOTTIME

On Wednesday, April 25, 2018 11:28:27 PM CEST Rafael J. Wysocki wrote:
> On Wednesday, April 25, 2018 9:09:29 PM CEST Thomas Gleixner wrote:
> > On Wed, 25 Apr 2018, Linus Torvalds wrote:
> > > On Wed, Apr 25, 2018 at 6:45 AM, tip-bot for Thomas Gleixner
> > > <tipbot@...or.com> wrote:
> > > >
> > > > As stated in the pull request for the unification of CLOCK_MONOTONIC and
> > > > CLOCK_BOOTTIME, it was clear that we might have to revert the change.
> > > 
> > > I'm ok with the revert., but I do want the revert message to talk
> > > about *exactly* what broke.
> > > 
> > > I don't see the reported watchdog things, and I run systemd and I ran
> > > these patches.
> > 
> > With suspend/resume?
> > 
> > > So it's not just "systemd uses this for a watchdog". It must be
> > > something specific that made it trigger for some people and not
> > > others, and it's that specific thing that we should document so that
> > > we know why this simplification failed.
> > 
> > Fair enough. Do the reporters have more information or do I have to chase
> > it down myself?
> 
> Well, if CLOCK_MONOTONIC did not count when the system was suspended and now
> it does that due to the change in question, then this is a significant
> difference in behavior likely to confuse things even in principle.

FWIW, here's a list of issues reported and narrowed down to the commit
in question so far I could find:

* systemd kills daemons on resume, after >WatchdogSec seconds
  of suspending (Genki Sky).  [Verified that that's because systemd uses
  CLOCK_MONOTONIC and expects it to not include the suspend time.]

* systemd-journald misbehaves after resume:
  systemd-journald[7266]: File /var/log/journal/016627c3c4784cd4812d4b7e96a34226/system.journal corrupted or uncleanly shut down, renaming and replacing.
  (	Mike Galbraith).

* NetworkManager reports "networking disabled" and networking is broken
  after resume 50% of the time (Pavel).  [May be because of systemd.]

* MATE desktop dims the display and starts the screensaver right after
  system resume (Pavel).

* Full system hang during resume (me).  [May be due to systemd or NM or both.]

I'm not sure if all of the above can be connected to one specific thing (other
than the fact that things get confused if they expect CLOCK_MONOTONIC to not
include system suspend time).