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kernel NULL pointer dereference when plugging in display

Brief summary of the problem:

Sometimes when plugging in a second display (by means of a hardware DisplayPort switch), the system will bug with a kernel NULL pointer dereference and lock up. The problem appears to have started happening with kernel 6.4.

Hardware description:

  • CPU: 5950X
  • GPU: VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Baffin [Radeon RX 550 640SP / RX 560/560X] [1002:67ff] (rev ff)
  • System Memory: 64GB
  • Display(s): 3440x1440 * 2 at the time of crash
  • Type of Display Connection: HDMI plugged in, DP plugging in

System information:

  • Distro name and Version: Debian Sid
  • Kernel version: 6.4.7 (first seen with 6.4.3, earlier versions not tested)

How to reproduce the issue:

Not always reproducible. The crash is always preceded by amdgpu 0000:0d:00.0: amdgpu: failed to get a new IB (-512) (see log below for more context) but this error also sometimes appears when plugging in a display without being followed by the NULL pointer dereference.

Log files (for system lockups / game freezes / crashes)

amdgpu_bug.log (log from 6.4.3 but problem still exists on 6.4.7; 6.4.8 does not appear likely to contain a fix)