[Bug 89727] New: [SKL] Test machine hang up when kill gnome-session two times

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89727

            Bug ID: 89727
           Summary: [SKL] Test machine hang up when kill gnome-session two
                    times
           Product: DRI
           Version: unspecified
          Hardware: All
                OS: Linux (All)
            Status: NEW
          Severity: critical
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: yex.tian at intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org,
                    mengmeng.meng at intel.com

System Environment:       
-----------------------------------------------------
Platform: SKL 
Regression: Not sure, this bug was introduced by fix another known issue:
bug-89388, we verified below commit (exist in drm-intel-next-queued branch) was
intent to fix bug-89388, but cause this issue.
The console show this error message:” [drm:gen8_irq_handler [i915]] *ERROR* CPU
pipe A FIFO underrun”

==Kernel==
--------------------------------------------------
commit c9f038a1a5924352ab8e510e4a45ac57b08db391
Author:     Matt Roper <matthew.d.roper at intel.com>
AuthorDate: Mon Mar 9 11:06:02 2015 -0700
Commit:     Daniel Vetter <daniel.vetter at ffwll.ch>
CommitDate: Tue Mar 17 22:30:17 2015 +0100

    drm/i915: Don't assume primary & cursor are always on for wm calculation
(v4)

    Current ILK-style watermark code assumes the primary plane and cursor
    plane are always enabled.  This assumption, along with the combination
    of two independent commits that got merged at the same time, results in
    a NULL dereference.  The offending commits are:Bug detailed description:
--------------------------------------------------

Reproduce steps:
----------------------------
1, Boot up system with edp display connected
2. xinit & 
3. gnome-session
4. kill x
5. Repeat step 2-4, will encounter machine hang up issue.

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