** Also affects: mir
Importance: Undecided
Status: New
** Changed in: mir (Ubuntu)
Assignee: Chris Halse Rogers (raof) => (unassigned)
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https://bugs.launchpad.net/bugs/1634888
Title:
Problems switching VTs
Status in Mir:
New
Status in mir package in Ubuntu:
New
Bug description:
I've hit an issue where LightDM trying to switch directly from a USC-
owned VT to an X-owned VT crashes X instead and doesn't switch VTs
after all.
I'm not sure exactly where the problem lies or exactly what the root
cause is. But here's my reproduction steps:
1) bileto host-upgrade 1679 # upgrades unity8 to have an in-session
lockscreen -- you must be in vivid, xenial, or zesty
2) sudo apt update && sudo apt upgrade
3) sudo apt install unity8-desktop-session
4) Reboot
5) Log one user into a unity7 session.
6) Switch users and log a separate user into a unity8 session.
7) In unity8, press Ctrl+L to show the in-session lockscreen and switch to
the unity7 user.
8) Usually this breaks things and the switch doesn't happen. Sometimes it
will work in which case switch back and forth until it does.
That's a bit of a pain, I understand. It's just the how I hit this
bug. I think switching directly from a USC-owned VT to an X-owned VT
is hitting a new and odd code path.
What happens under the cover that I've found is that X fails during
EnterVT and aborts. Which confuses everyone else, including lightdm.
RAOF says "The hypothesis is that Mir fails to drop master for
whatever reason, which results in it (correctly) NAKing the VT switch.
(We call drmDropMaster, but that can fail; if it does, we throw an
exception, (silently) catch it, and NAK the VT switch)"
I have a USC log with MIR_SERVER_DISPLAY_REPORT=log set (though I
can't see any display report spew...?) but it's not very revealing:
http://paste.ubuntu.com/23348320
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