[Bug 107738] New: System hangs when hot-plugging Thunderbolt 3 dock with dual output (DP MST) connected

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107738

            Bug ID: 107738
           Summary: System hangs when hot-plugging Thunderbolt 3 dock with
                    dual output (DP MST) connected
           Product: DRI
           Version: unspecified
          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: leo at grange.cafe
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 141349
  --> https://bugs.freedesktop.org/attachment.cgi?id=141349&action=edit
Kernel log from journalctl output

-- chipset: Intel HD Graphics 520 (GT2)
-- system architecture: x86_64
-- xorg-server: 1.20.1 (using generic modesetting driver)
-- libdrm: 2.4.93
-- kernel version: 4.18.5-arch1-1-ARCH
-- Linux distribution: Archlinux
-- Machine: Lenovo T470 20JN (Intel Core i5-6300U)
-- Display connector: HDMI over DP MST adapter plugged on Thunderbolt 3 port
-- Adapter reference: Cable Matters USB-C Multiport Travel Dock with Dual HDMI
and PD

When plugging the TB3 dock with two monitors already attached to it, the system
hangs (unable to switch to a TTY or to blind-logging to reboot cleanly).
If the dock is plugged before booting, everything is working fine including the
two monitors.
Additionally, if only one monitor is attached to the dock, the hot-plugging
appears to work too.

I am not sure of the root cause of the issue, as the kernel shows several Oops,
one of them being in Xorg process context (see below and attachment), but I
think the problem is either in the generic DRM/KMS code or in the Intel DRM
code.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000320
CPU: 2 PID: 1216 Comm: Xorg Tainted: G           O      4.18.5-arch1-1-ARCH #1
[...]
Call Trace:
drm_dp_mst_wait_tx_reply+0x13e/0x1e0 [drm_kms_helper]
[...]
? drm_mode_connector_property_set_ioctl+0x60/0x60 [drm]


I attached the kernel log from journalctl, the dock was re-connected at
16:32:30 (line 1029 in the log).
I don't have much time these days, but I will do my best to try to reproduce
the bug with the drm-tip branch and to update the issue as soon as I have new
inputs.
Please let me know if some other information is required.

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