Bug#861956: X server hangs at shutdown if it's in background
Package: xserver-xorg-core
Version: 2:1.19.2-1
Tags: patch
Dear Maintainers,
When X server is in background (i.e. when its tty is not active), it
doesn't react to SIGTERM and causes a shutdown delay.
I first noticed this after disabling Wayland in GDM by uncommenting
`WaylandEnable=false' in /etc/gdm3/daemon.conf. In this configuration
GDM uses X server (and doesn't shut it down when starting a user
session, so there are two X servers running: one for user session
(foreground), and still one for GDM (background)).
When I shut the machine down right from GDM without logging in, it went
OK. However, if I logged in and issued reboot from inside the user
session, shutdown was delayed for about 1 and a half minute, with the
following message in console: `A stop job is running for Session c1 of
user Debian-gdm'.
I enabled debug-shell.service, and here is what I got:
# loginctl session-status c1
c1 - Debian-gdm (114)
Since: Thu 2017-05-04 21:47:00 MSK; 10min ago
Leader: 502
Seat: seat0; vc1
TTY: /dev/tty1
Service: gdm-launch-environment; type x11; class greeter
State: closing
Unit: session-c1.scope
`-515 /usr/lib/xorg/Xorg vt1 -displayfd 3 -auth /run/user/114/gdm/Xauthority -background none -noreset -keeptty -verbose 3
May 04 21:49:15 debian /usr/lib/gdm3/gdm-x-session[513]: (II) systemd-logind: got pause for 13:65
May 04 21:49:15 debian /usr/lib/gdm3/gdm-x-session[513]: (II) systemd-logind: got pause for 13:67
May 04 21:49:15 debian /usr/lib/gdm3/gdm-x-session[513]: (II) systemd-logind: got pause for 13:69
May 04 21:49:15 debian /usr/lib/gdm3/gdm-x-session[513]: (II) systemd-logind: got pause for 13:71
May 04 21:49:15 debian /usr/lib/gdm3/gdm-x-session[513]: (II) systemd-logind: got pause for 13:68
May 04 21:49:15 debian /usr/lib/gdm3/gdm-x-session[513]: (II) systemd-logind: got pause for 13:64
May 04 21:49:15 debian /usr/lib/gdm3/gdm-x-session[513]: (II) systemd-logind: got pause for 226:0
May 04 21:57:08 debian gnome-session-binary[523]: WARNING: Lost name on bus: org.gnome.SessionManager
May 04 21:57:08 debian gnome-session[523]: gnome-session-binary[523]: WARNING: Lost name on bus: org.gnome.SessionManager
May 04 21:57:08 debian systemd[1]: Stopping Session c1 of user Debian-gdm.
As you see, the X server was still running. `kill -s SIGTERM 515' had
no effect. It required SIGKILL to shut down the process.
`pstree' gave the following output:
# pstree
systemd-+-NetworkManager-+-{gdbus}
| `-{gmain}
|-Xorg---{InputThread}
|-bash-+-pstree
| `-shutdown
|-dbus-daemon
|-dhclient
|-systemd-journal
|-systemd-logind
`-systemd-udevd
Looked like the InputThread thread was still running. It was confirmed
after attaching GDB to the server process at next shutdown (hence a
different PID):
# gdb --pid=536
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Attaching to process 536
[New LWP 542]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007f3851d5e6cd in pthread_join (threadid=139879650666240,
thread_return=thread_return@entry=0x0) at pthread_join.c:90
(gdb) info threads
Id Target Id Frame
* 1 Thread 0x7f385408ba40 (LWP 536) "Xorg" 0x00007f3851d5e6cd in pthread_join (
threadid=139879650666240, thread_return=thread_return@entry=0x0) at pthread_join.c:90
2 Thread 0x7f3844e3a700 (LWP 542) "InputThread" __lll_lock_wait ()
at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
(gdb) bt
#0 0x00007f3851d5e6cd in pthread_join (threadid=139879650666240,
thread_return=thread_return@entry=0x0) at pthread_join.c:90
#1 0x000055d6880e63f0 in InputThreadFini () at ../../../../os/inputthread.c:500
#2 0x000055d687f816a6 in dix_main (argc=12, argv=0x7fff890930c8, envp=<optimized out>)
at ../../../../dix/main.c:312
#3 0x00007f38519d82b1 in __libc_start_main (main=0x55d687f6b260 <main>, argc=12,
argv=0x7fff890930c8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>,
stack_end=0x7fff890930b8) at ../csu/libc-start.c:291
#4 0x000055d687f6b29a in _start ()
(gdb) thread 2
[Switching to thread 2 (Thread 0x7f3844e3a700 (LWP 542))]
#0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
(gdb) bt
#0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
#1 0x00007f3851d5fc06 in __GI___pthread_mutex_lock (
mutex=mutex@entry=0x55d68837de60 <input_mutex>) at ../nptl/pthread_mutex_lock.c:115
#2 0x000055d6880e5c80 in input_lock () at ../../../../os/inputthread.c:113
#3 0x000055d6880e5df5 in InputThreadDoWork (arg=<optimized out>)
at ../../../../os/inputthread.c:343
#4 0x00007f3851d5d494 in start_thread (arg=0x7f3844e3a700) at pthread_create.c:333
#5 0x00007f3851aa093f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:97
(gdb)
So, the main thread waited for the input thread to quit while the latter
was locked in pthread_mutex_lock().
After searching a bit, I found a suspicious function xf86VTLeave() at
file hw/xfree86/common/xf86Events.c, line 411 [1], which locked input
mutex, but didn't unlock it at execution path when function
xf86VTSwitchAway() at line 450 returned true. Indeed, after adding
input_unlock() before return, I can't reproduce the issue anymore.
Patch is attached.
[1] https://sources.debian.net/src/xorg-server/2:1.19.3-1/hw/xfree86/common/xf86Events.c/#L411
--
Алексей Шилинdiff -aNru xorg-server-1.19.2.orig/hw/xfree86/common/xf86Events.c xorg-server-1.19.2/hw/xfree86/common/xf86Events.c
--- xorg-server-1.19.2.orig/hw/xfree86/common/xf86Events.c 2017-03-03 02:03:58.000000000 +0300
+++ xorg-server-1.19.2/hw/xfree86/common/xf86Events.c 2017-05-06 14:57:25.184007000 +0300
@@ -468,6 +468,8 @@
xf86UpdateHasVTProperty(FALSE);
+ input_unlock();
+
return;
switch_failed:
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