Created attachment 120038 [details]
strace for xset q
I run xorg as a socket activated systemd service. Since I upgraded to version 1.18 of the X server, socket activation does not work. It all worked as expected in 1.17.
The client that triggers the socket-activation, gets stuck. Here is a way to reproduce the problem from the command line on a linux system running systemd:
$ /usr/lib/systemd/systemd-activate -l /tmp/.X11-unix/X0 /usr/bin/Xorg :0 -nolisten tcp -noreset -verbose 3 vt2 &
$ DISPLAY=:0 xset q
The first line emulates socket activation, by waiting on the socket and launching the X server on first connection.
When the second line is executed, it triggers the xorg activation correctly, the X server starts without problems, but xset gets stuck (never returns).
Other invocations of xset q after the server is already started work as expected.
I attach an strace for the xset command in the getting-stuck scenario.
I'm seeing this as well.
In which distro release did you observe this problem?
I've also observed it in Ubuntu 15.10 (which ships Xorg 1.17.2 and systemd 225), but it does work in openSUSE Leap 42.1 (which also ships Xorg 1.17.2, but stays on systemd 210). I'll repeat the tests in Ubuntu 16.04 beta 1 and openSUSE Tumbleweed.
I've tested Xorg socket activation in Ubuntu 16.04 beta1 (xorg-server 1.17.3 + systemd 229) and openSUSE Tumbleweed (xorg-server 1.18.1 + systemd 228). One more time, Ubuntu is affected by this bug, but openSUSE is not.
I'm running arch linux.
At the time I reported this, I was running systemd 227 or 228, I can't tell exactly, because arch pushed 228 at around that time too.
I'm pretty sure though, that the issue manifested itself after upgrading xorg from 1.17 to 1.18. I noticed the problem immediately, because at that time my window manager was running on a socket activated xorg. It broke my system.
I've just tested it again with systemd 229 and xorg 1.18.1. The issue persists, however now the whole vt system gets frozen. I can't even change vt with Ctrl+Alt+Fn after the two commands I suggested.
It is possible that systemd-logind is involved, or maybe I'm now seeing two different issues...
I'll try to get more useful data and report back.
I'm also running arch (systemd 229, xorg 1.18). A quick fix is to make sure, that the xorg server is started before any units that require it get started. See https://www.reddit.com/r/archlinux/comments/3twekg/xorg_118_messes_with_socket_activation_in_systemd/
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