[Bug 91438] New: hard lockup after switching between laptop's panel and external monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91438

            Bug ID: 91438
           Summary: hard lockup after switching between laptop's panel and
                    external monitor
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: ivan.mitev at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 117314
  --> https://bugs.freedesktop.org/attachment.cgi?id=117314&action=edit
relevant dmesg and laptop info

When docking my laptop I usually use xrandr to turn off the laptop's display so
that my taskbar and network applets are displayed properly on my external
monitor.
When trying to debug some unrelated stuff I found out that I could hard lock
the laptop after switching back and forth a few times between both monitors.

It took quite a bit of time to reproduce the problem. It happens only when the
laptop is docked.

How to reproduce:
- laptop docked, external monitor on VGA port (no dongle)
- the following steps trigger a hard lockup:

# "try1"
xrandr --output $PANEL --off
xrandr --output $EXT --auto
xrandr --output $PANEL --auto
xrandr --output $EXT --off

# "try2"
xrandr --output $PANEL --off
xrandr --output $EXT --auto # the external panel stays blank
xrandr --output $PANEL --auto # locks a bit after here
xrandr --output $EXT --off

note that the blocks are identical - ie there's no problem the first time, but
running the same commands a second time trigger the lockup. Both displays are
black/blank so there's no way to even see what's happening.

The xrandrvga script in the attached tgz outputs dmesg + xrandr --verbose after
each switch. The debug files show that the output of xrandr --verbose after
setting the panel to auto in the 2nd "try" is 0. So I'm not sure if it's
because of running xrandr, or because the next command (turning off the
external panel) triggers the hard lockup and the output file is not flushed to
disk.

note:
- when docked, the external monitor shows up as DP2-3, and it's DP2 when
undocked (= plugged in the laptop's VGA port).
- enable_psr=0, enable_fbc=0

Hardware: lenovo T450s, model 20BX000TBM (see attached dmidecode and lspci_vv).
OS: Fedora 22, fully updated (as of 2015-07-23)
Kernel: git drm-intel-nightly (as of 2015-07-22 evening). .config attached
(config.drm-intel).
Xorg:
- xorg-x11-server-Xorg-1.17.2-1.fc22.x86_64
- xorg-x11-drv-intel-2.99.917-12.20150615.fc22.x86_64
- mesa-dri-drivers-10.6.1-1.20150629.fc22.x86_64

attached a tgz with the relevant files
- docked: tests with the laptop docked (lockup)
- undocked_on_AC: tests with the laptop undocked, on AC, with the external
monitor plugged in the laptop's VGA port. (in that case everything is working
fine).

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