kdeinit freezes on Wayland in OOM protection

[Martin Graesslin]

On Friday, November 27, 2015 1:05:26 PM CET Michael Pyne wrote:
> On Thu, November 26, 2015 13:16:04 Martin Graesslin wrote:
> > we are facing a problem during the startup of Plasma on Wayland. If OOM
> > protection is enabled for kdeinit and we already have a running X server,
> > kdeinit freezes dead.
> > 
> > I'm sorry for having ignored the issue for too long and had just disabled
> > OOM protection on my system, so I never hit it. Now I enabled it again to
> > get the problem. On my system I have now two frozen kdeinit processes:
> > 
> > martin    1960  1956  0 77832 26448   1 13:05 ?        00:00:00
> > /opt/kf5/bin/ kdeinit5 --oom-pipe 4 --kded +kcminit_startup
> > martin    1961  1960  0 77832  2816   3 13:05 ?        00:00:00
> > /opt/kf5/bin/ kdeinit5 --oom-pipe 4 --kded +kcminit_startup
> > 
> > One has the following stacktrace:
> > It's frozen in this line of code:
> > sigsuspend(&oldsigs);   // wait for the signal to come
> > 
> > The other one has the following stacktrace:
> > which is:
> > d.n = read(d.fd[0], &d.result, 1);
> > 
> > Given that it looks to me like these two processes dead-lock. I do not
> > understand why, why it only happens on Wayland, why the fact that an X
> > server must already be running is relevant and what the OOM protection has
> > to do with it.
> 
> I don't have the answer but I can help explain the deadlock better I think.

thanks for your input. It helped me understanding quite a bit.

Some more testing results:
Weston+Xwayland: doesn't show the problem
Weston without Xwayland (and DISPLAY=$WAYLAND_DISPLAY): doesn't show the 
problem.

What I absolutely do not understand how KWin could influence it. From all the 
backtraces I see it always freezes before interacting with the windowing 
system.

Any more ideas to test and investigate, highly appreciated. I got a rather 
high number of complaints due to that problem and it's a showstopper and I'm 
lost with it.

Cheers
Martin
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