[regression] mir_demo_server refuses to quit on Ctrl+Alt+Backspace or Ctrl+C in its terminal (deadlock in DefaultInputDeviceHub::add_device)

Bisected. The regression started here:

------------------------------------------------------------
revno: 4002 [merge]
author: Andreas Pokorny <email address hidden>
committer: Tarmac
branch nick: development-branch
timestamp: Wed 2017-02-01 17:32:36 +0000
message:
  mir_connection_apply_input_configuration and mir_connection_set_base_input_configuration

  This adds two new mirclient functions to configure input devices. The base input configuration behaves like the base display configuration.
  .

  Approved by Alan Griffiths, mir-ci-bot.
------------------------------------------------------------

The problem is that the main loop never exists. I'm guessing we now have a source that never shuts up.

This is the cause...

#0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
#1 0x00007f08e1a65ebd in __GI___pthread_mutex_lock (mutex=0x2823fd0) at ../nptl/pthread_mutex_lock.c:80
#2 0x00007f08e017e8e3 in __gthread_mutex_lock (__mutex=0x2823fd0)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0/bits/gthr-default.h:748
#3 0x00007f08e017eaa5 in std::mutex::lock (this=0x2823fd0)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/bits/std_mutex.h:103
#4 0x00007f08e01a387c in std::unique_lock<std::mutex>::lock (this=0x7ffe8ab8edc8)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/bits/std_mutex.h:267
#5 0x00007f08e019ea44 in std::unique_lock<std::mutex>::unique_lock (this=0x7ffe8ab8edc8, __m=...)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/bits/std_mutex.h:197
#6 0x00007f08e0211697 in mir::input::DefaultInputDeviceHub::device_changed (this=0x2823fa0, dev=
    0x7f08c8014f80) at /home/alan/display_server/mir/src/server/input/default_input_device_hub.cpp:338

****************>>> std::unique_lock<std::mutex> lock(observer_guard);

#7 0x00007f08e0212820 in mir::input::DefaultInputDeviceHub::add_device(std::shared_ptr<mir::input::InputDevice> const&)::$_1::operator()(mir::input::Device*) const (this=0x7f08c8015068, d=0x7f08c8014f80)
    at /home/alan/display_server/mir/src/server/input/default_input_device_hub.cpp:78
#8 0x00007f08e02126d2 in std::_Function_handler<void (mir::input::Device*), mir::input::DefaultInputDeviceHub::add_device(std::shared_ptr<mir::input::InputDevice> const&)::$_1>::_M_invoke(std::_Any_data const&, mir::input::Device*&&) (__functor=...,
    __args=<unknown type in cmake-build-debug/bin/../lib/libmirserver.so.44, CU 0x17fea7, DIE 0x1984b4>)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/functional:1731
#9 0x00007f08e020cef8 in std::function<void (mir::input::Device*)>::operator()(mir::input::Device*) const
    (this=0x7f08c8015068, __args=0x7f08c8014f80)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/functional:2127
#10 0x00007f08e020b11b in mir::input::DefaultDevice::apply_pointer_configuration (this=0x7f08c8014f80,
    conf=...) at /home/alan/display_server/mir/src/server/input/default_device.cpp:136
#11 0x00007f08e091988b in mir::examples::InputDeviceConfig::device_added (this=0x2788a10, device=warning: RTTI symbol not found for class 'std::_Sp_counted_ptr_inplace<mir::input::DefaultDevice, std::allocator<mir::input::DefaultDevice>, (__gnu_cxx::_Lock_policy)2>'
warning: RTTI symbol not found for class 'std::_Sp_counted_ptr_inplace<mir::input::DefaultDevice, std::allocator<mir::input::DefaultDevice>, (__gnu_cxx::_Lock_policy)2>'

std::shared_ptr (count 3, weak 0) 0x7f08c8014f80)
    at /home/alan/display_server/mir/examples/server_example_input_device_config.cpp:187
#12 0x00007f08e0211136 in mir::input::DefaultInputDeviceHub::add_device_handle (this=0x2823fa0, handle=warning: RTTI symbol not found for class 'std::_Sp_counted_ptr_inplace<mir::input::DefaultDevice, std::allocator<mir::in...

Cool. I had noticed some server threads hung/deadlocked there recently and not realised it was this bug.

Bumped to High since Alan found it's a general deadlock in the server.

Fix committed into lp:mir at revision None, scheduled for release in mir, milestone 1.0.0

This bug was fixed in the package mir - 0.27.0+17.10.20170630-0ubuntu1

---------------
mir (0.27.0+17.10.20170630-0ubuntu1) artful; urgency=medium

  [ Daniel van Vugt ]
  * New upstream release 0.27.0 (https://launchpad.net/mir/+milestone/0.27.0)
    - ABI summary:
      . mirclient ABI unchanged at 9
      . mirserver ABI bumped to 44
      . mircommon ABI unchanged at 7
      . mirplatform ABI bumped to 61
      . mirprotobuf ABI unchanged at 3
      . mirplatformgraphics ABI bumped to 13
      . mirclientplatform ABI unchanged at 5
      . mirinputplatform ABI bumped to 7
      . mircore ABI unchanged at 1
    - Enhancements:
      . Mostly groundwork required to support major enhancements coming in
        future Mir versions.
      . Removed android-input and eliminated the entire "3rd_party/" subtree.
        Now the Mir source tree contains original code only.
      . Added mir_prompt_session_new_fds_for_prompt_providers_sync API.
      . mirout: Added load and save options for keeping display configs
        on disk.
      . mirout: Added "--" support for applying configuration changes under
        Unity8.
      . Fixed failure of DRM hardware cursor {hide(); show(image);}
      . Added server option: "--cursor software" (MIR_SERVER_CURSOR=software)
      . Added letterboxing/black bars support to the GL renderer in preparation
        for generic output cloning.
      . Added client API for getting the logical size of an output.
      . Migrated MirCookie to use SHA-256.
      . Ensure RealKMSOutputConfiguration stays in sync with actual hardware
        state.
      . Added support for drag-and-drop.
      . Lots of other client API enhancements.
      . Minor clean-ups, optimizations and dead code removal.
      . Added support for building on Ubuntu 17.10 artful.
      . Update example code to use undeprecated API.
      . mesa-kms: Support hardware cursors in hybrid setups.
      . Rework and publish the graphics platform APIs
    - Bugs fixed:
      . [enhancement] Make able to get version information from client /
        server APIs (LP: #1195540)
      . Touch screen coordinates don't rotate with the screen (LP: #1349660)
      . Subpixel order not included in Mir display information (LP: #1393578)
      . [enhancement] Missing client API for relative surface movement (e.g.
        dragging client-decorated windows) (LP: #1420334) . Mir does not reset
        key states when paused or resumed (modifiers get stuck after VT
        switching) (LP: #1536279)
      . NBS never uses mc::MultiMonitorMode::single_monitor_fast, even when
        only a single monitor is plugged in (LP: #1561418)
      . Inconsistent behaviour of Num Lock (LP: #1588237)
      . A scaled (not panned or clipped) mirror/clone mode is desired
        (LP: #1639226)
      . Rotating an output left or right without restarting the
        compositor distorts the image (LP: #1643488)
      . support display scaling slider in unity8 (LP: #1645372)
      . [ FAILED ] NestedInputWithMouse.mouse_pointer_coordinates_in_nested_
        server_are_accumulated (LP: #1646375)
      . [ FAILED ] NestedInputWithMouse.mouse_pointer_position_is_in_sync_with_
        ho...