[Bug 203879] New: hard freeze on high single threaded load when Xorg is active (AMD Ryzen 7 2700X CPU, AMD Radeon RX 580 GPU)

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=203879

            Bug ID: 203879
           Summary: hard freeze on high single threaded load when Xorg is
                    active (AMD Ryzen 7 2700X CPU, AMD Radeon RX 580 GPU)
           Product: Drivers
           Version: 2.5
    Kernel Version: 4.19.37-3 (Debian 4.19.0-5-amd64) and others
                    (including mainline versions)
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri@kernel-bugs.osdl.org
          Reporter: claude@mathr.co.uk
        Regression: No

Created attachment 283233
  --> https://bugzilla.kernel.org/attachment.cgi?id=283233&action=edit
dmesg from 4.19.0-5-amd64 with amdgpu.dc=1 (no freeze yet)

I am developing a CPU-based program to render fractals, which I usually run
with "nice -n 20".  The main calculations are multi-threaded, using 16 threads
on AMD Ryzen 7 2700X Eight-Core Processor.  However, final image PNG saving is
single-threaded.  During the single-threaded workload only (as observed by htop
and program status prints), it can happen that the system freezes hard (no ssh,
stuck mouse pointer, no NumLock LED toggle, no magic SysRq, only physical power
button for hard power-off works).

This freeze only happens when Xorg is running on the active virtual terminal: I
tried to see if some kernel log messages would be displayed before freeze by
switching to a console with Ctrl-Alt-F1 after launching my program, but with
the terminal active it doesn't seem to freeze.

The freeze does not always occur, but usually happens before a dozen images are
saved (sequential process is full-threaded workload, followed by
single-threaded workload, repeated).  This can take a few hours.

With the virtual terminal active instead of Xorg, I have rendered 100+ images
in a row without any issues.  Of course, I can't use other X applications at
the same time, so this is an annoying workaround.

I mostly run the regular Debian Buster kernel but I have had this freeze occur
with other self-compiled kernels of various versions (newer than the Debian
kernel, without Debian patches).  I also had the freeze with both amdgpu.dc=1
(default) and amdgpu.dc=0 options.

$ uname -a
Linux eiskaffee 4.19.0-5-amd64 #1 SMP Debian 4.19.37-3 (2019-05-15) x86_64
GNU/Linux

$ apt-cache policy linux-image-4.19.0-5-amd64
linux-image-4.19.0-5-amd64:
  Installed: 4.19.37-3
  Candidate: 4.19.37-3
  Version table:
 *** 4.19.37-3 990
        990 http://ftp.uk.debian.org/debian buster/main amd64 Packages
        500 http://ftp.uk.debian.org/debian unstable/main amd64 Packages
        100 /var/lib/dpkg/status

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