unity8 crash on unplug of monitor

[kevin gunn]

Stability of hotplug is much better - so this is not a duplicate of bug 1488863
Maybe every 1/4 unplug event will see unity8 crash....strangely, didn't capture a crash log until now.

This configuration is
latest PD image + silo 18 (with point release fixes for Mir0.17)
also libertine/puritine installed
xmir is from libertine devel ppa

[kevin gunn (kgunn72)]

OK, on an updated PD image with silo 18 I am seeing this very consistently now.
Mainly on plugging in the monitor now. Greater than 50% of the time.
Attaching crash file i'm seeing consistently.

[Gerry Boland (gerboland)]

Investigating, after hotplugging a second monitor, it appears that sometimes Mir has only 1 display buffer ready, when there should be 2 - one for each screen. Need to ask Mir team help

[Gerry Boland (gerboland)]

http://bazaar.launchpad.net/~mir-team/qtmir/trunk/view/head:/src/platforms/mirserver/screencontroller.cpp#L157 is the relevant line of code. This triggers after compositor start, to match mir DisplayBuffers with Qt Screens. I've designed it under the assumption that each Mir Display will always have a DisplayBuffer on compositor start.

[Alan Griffiths (alan-griffiths)]

There's a whole host of Mir bugs in this area due to races detecting and responding to display configuration changes (either from hardware changes or from a session getting focus) with the creation of the nested servers fullscreen surfaces. A chunk of these are fixed by lp:~alan-griffiths/mir/fix-1506846 - but there's probably more to come.

[Gerry Boland (gerboland)]

http://pastebin.ubuntu.com/13216662/ is useful log. It indicates that 2 displays are detected by mir, and are not being cloned. However it appears that there is only a single DisplayBuffer available (Screen::setMirDisplayBuffer should be called for each DisplayBuffer, but only called once)