u-s-c crashes on first boot on flo, stuck on Google boot screen

in /var/log/lightdm/unity-system-compositor.log:

root@ubuntu-phablet:/var/log/lightdm# cat unity-system-compositor.log
GL_VENDOR = Qualcomm
GL_RENDERER = Adreno (TM) 320
GL_VERSION = OpenGL ES 3.0 V@53.0 AU@ (CL@)
dm_connection_start
set_active_session 'session-0'
set_active_session
Unable to set active session, unknown client name session-0

When running u-s-c by hand:
root@ubuntu-phablet:~# strace unity-system-compositor --file /tmp/mir_socket
execve("/usr/sbin/unity-system-compositor", ["unity-system-compositor", "--file", "/tmp/mir_socket"], [/* 34 vars */]) = 0
brk(0) = 0x1560000
uname({sys="Linux", node="ubuntu-phablet", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb6fec000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
...
open("/root/.config/unity-system-compositor.conf", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)
open("/etc/xdg/unity-system-compositor.conf", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)
eventfd2(0, O_NONBLOCK|O_CLOEXEC) = 3
epoll_create1(EPOLL_CLOEXEC) = 4
timerfd(1, 0x80000 /* CLOCK_??? */, TFD_TIMER_ABSTIME|0xfffffffe, NULL) = 5
epoll_ctl(4, EPOLL_CTL_ADD, 3, {EPOLLIN|EPOLLERR|EPOLLET, {u32=22461928, u64=22461928}}) = 0
write(3, "\1\0\0\0\0\0\0\0", 8) = 8
epoll_ctl(4, EPOLL_CTL_ADD, 5, {EPOLLIN|EPOLLERR, {u32=22461940, u64=22461940}}) = 0
epoll_ctl(4, EPOLL_CTL_ADD, -1, {EPOLLIN|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET, {u32=22461992, u64=22461992}}) = -1 EBADF (Bad file descriptor)
close(4) = 0
close(5) = 0
close(3) = 0
write(2, "ERROR: ", 7ERROR: ) = 7
write(2, "Throw location unknown (consider"..., 248Throw location unknown (consider using BOOST_THROW_EXCEPTION)
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::system::system_error> >
std::exception::what: assign: Bad file descriptor
) = 248
write(2, "\n", 1
) = 1
futex(0xb6fbd824, FUTEX_WAKE_PRIVATE, 2147483647) = 0
futex(0xb6dc8f6c, FUTEX_WAKE_PRIVATE, 2147483647) = 0
futex(0xb68e62c8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
exit_group(1) = ?
+++ exited with 1 +++

Also what is available in /var/log/lightdm/unity-system-compositor.log:
ERROR: /build/buildd/mir-0.1.5+14.04.20140212/src/platform/graphics/android/android_alloc_adaptor.cpp(68): Throw in function virtual std::shared_ptr<mir::graphics::NativeBuffer> mir::graphics::android::AndroidAllocAdaptor::alloc_buffer(mir::geometry::Size, MirPixelFormat, mir::graphics::android::BufferUsage)
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::runtime_error> >
std::exception::what: buffer allocation failed

[+0.01s] DEBUG: Logging to /var/log/lightdm/lightdm.log
[+0.01s] DEBUG: Starting Light Display Manager 1.9.8, UID=0 PID=881
[+0.01s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf
[+0.01s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-guest-wrapper.conf
[+0.01s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-xserver-command.conf
[+0.01s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf.d/52-ubuntu-touch.conf
[+0.01s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf.d/90-phablet.conf
[+0.01s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
[+0.01s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
[+0.01s] DEBUG: Registered seat module xlocal
[+0.01s] DEBUG: Registered seat module xremote
[+0.01s] DEBUG: Registered seat module unity
[+0.01s] DEBUG: Registered seat module surfaceflinger
[+0.08s] DEBUG: Adding default seat
[+0.09s] DEBUG: Using VT 1
[+0.09s] DEBUG: DisplayServer: Logging to /var/log/lightdm/unity-system-compositor.log
[+0.09s] DEBUG: Launching process 919: /usr/share/ubuntu-touch-session/usc-wrapper --file '/tmp/mir_socket' --from-dm-fd 8 --to-dm-fd 14 --vt 1
[+0.09s] DEBUG: DisplayServer: Waiting for system compositor for 60s
[+0.09s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+0.09s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
[+0.44s] DEBUG: Loading users from org.freedesktop.Accounts
[+0.44s] DEBUG: User /org/freedesktop/Accounts/User1002 added
[+0.68s] DEBUG: User /org/freedesktop/Accounts/User32011 added
[+0.75s] DEBUG: User /org/freedesktop/Accounts/User1003 added
[+0.82s] DEBUG: DisplayServer: Compositor closed communication channel
[+0.82s] DEBUG: Process 919 exited with return value 1

This bug was fixed in the package ubuntu-touch-session - 0.103

---------------
ubuntu-touch-session (0.103) trusty; urgency=medium

  * lightdm.override: adding dependency again on runlevel, otherwise
    unity-system-compositor fails to start on flo (LP: #1283326)
 -- Ricardo Salveti de Araujo <email address hidden> Sat, 22 Feb 2014 00:02:25 -0300

opening a task against lightdm, we need to identify why we need to delay the startup by nearly two seconds (which depending on runlevel does ... we do not use runlevels and should have a proper dependency chain instread) and add a proper dependency to the upstart override job for the actually needed prerequisite.

It would also be intresting to know why the demo image behaves different here, I tested this change against an Image from the normal archive builds where it did not expose any issues on flo.