sddm hangs at __GI___poll (...) at ../sysdeps/unix/sysv/linux/poll.c:41

When booting to "graphical.target" sddm hangs with a flashing text mode cursor at the bottom of tty1. Running "startx" on tty2 successfully starts KDE/Plasma (sddm remains hung).

The the sddm status provided below shows that the sddm start did not finish. The gdm back-trace below shows that sddm hung in __GI___poll (...) at ../sysdeps/unix/sysv/linux/poll.c:41.

The Ubuntu install is kubuntu-desktop on Ubuntu server 19.10 (64bit) on a 4GB Rasperrypi 4. Note that the same behaviour occurs on the 20.04 daily builds.

--//--

ubuntu@ubuntu:~$ systemctl status sddm
● sddm.service - Simple Desktop Display Manager
   Loaded: loaded (/lib/systemd/system/sddm.service; indirect; vendor preset: enabled)
   Active: active (running) since Sun 2020-03-01 15:07:30 AST; 22min ago
     Docs: man:sddm(1)
           man:sddm.conf(5)
  Process: 1489 ExecStartPre=/bin/sh -c [ "$(cat /etc/X11/default-display-manager 2>/dev/null)" = "/usr/bin/sddm" ] (code=exited, status=0/SUCCESS)
 Main PID: 1493 (sddm)
    Tasks: 2 (limit: 4429)
   CGroup: /system.slice/sddm.service
           └─1493 /usr/bin/sddm

Mar 01 15:07:29 ubuntu systemd[1]: Starting Simple Desktop Display Manager...
Mar 01 15:07:30 ubuntu systemd[1]: Started Simple Desktop Display Manager.
Mar 01 15:07:44 ubuntu sddm[1493]: Initializing...
Mar 01 15:07:44 ubuntu sddm[1493]: Starting...
Mar 01 15:07:44 ubuntu sddm[1493]: Logind interface found
ubuntu@ubuntu:~$

--//--

ubuntu@ubuntu:~$ ps -ax | grep sddm
 1493 ? Ssl 0:00 /usr/bin/sddm
 4524 ? Sl 0:53 /usr/lib/firefox/firefox https://bugs.launchpad.net/ubuntu/+source/sddm/+filebug/b170d010-5bf1-11ea-b34a-002481e7f48a?
 4903 pts/1 S+ 0:00 grep --color=auto sddm
ubuntu@ubuntu:~$ sudo gdb -p 1493
GNU gdb (Ubuntu 8.3-0ubuntu1) 8.3
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Attaching to process 1493
[New LWP 1563]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/aarch64-linux-gnu/libthread_db.so.1".
0x0000ffff99009a3c in __GI___poll (fds=0xaaaad31075b0, nfds=5, timeout=<optimized out>) at ../sysdeps/unix/sysv/linux/poll.c:41
41 ../sysdeps/unix/sysv/linux/poll.c: No such file or directory.
(gdb) bt
#0 0x0000ffff99009a3c in __GI___poll (fds=0xaaaad31075b0, nfds=5, timeout=<optimized out>) at ../sysdeps/unix/sysv/linux/poll.c:41
#1 0x0000ffff98651d54 in g_main_context_poll (priority=<optimized out>, n_fds=5, fds=0xaaaad31075b0, timeout=<optimized out>, context=0xaaaad30f0750)
    at ../../../glib/gmain.c:4216
#2 g_main_context_iterate (context=context@entry=0xaaaad30f0750, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>)
    at ../../../glib/gmain.c:3912
#3 0x0000ffff98651e7c in g_main_context_iteration (context=0xaaaad30f0750, may_block=may_block@entry=1) at ../../../glib/gmain.c:3978
#4 0x0000ffff99582884 in QEventDispatcherGlib::processEvents (this=0xaaaad30efdc0, flags=...) at kernel/qeventdispatcher_glib.cpp:424
#5 0x0000ffff99524ce8 in QEventLoop::exec (this=this@entry=0xfffff32b7cb0, flags=..., flags@entry=...)
    at ../../include/QtCore/../../src/corelib/global/qflags.h:140
#6 0x0000ffff9952d3bc in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:120
#7 0x0000aaaac3159d08 in main (argc=<optimized out>, argv=0xfffff32b7ed8) at ./src/daemon/DaemonApp.cpp:138
(gdb)

--//--

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: sddm 0.18.0-1ubuntu2
ProcVersionSignature: User Name 5.3.0-1018.20-raspi2 5.3.18
Uname: Linux 5.3.0-1018-raspi2 aarch64
ApportVersion: 2.20.11-0ubuntu8.4
Architecture: arm64
CurrentDesktop: KDE
Date: Sun Mar 1 15:17:21 2020
SourcePackage: sddm
UpgradeStatus: No upgrade log present (probably fresh install)