I had the same problem with Ubuntu 20.04 LTSP client: black screen during boot, keyboard and mouse don't work, ssh works and "ring 0 stalled" messages in the system log. I had to switch to Ubuntu 18.04 which works fine.
CPU: AMD A8-5500B APU with Radeon(tm) HD Graphics lshw -C display *-display description: VGA compatible controller product: Trinity [Radeon HD 7560D] vendor: Advanced Micro Devices, Inc. [AMD/ATI] physical id: 1 bus info: pci@0000:00:01.0 version: 00 width: 32 bits clock: 33MHz capabilities: pm pciexpress msi vga_controller bus_master cap_list rom configuration: driver=radeon latency=0 resources: irq:35 memory:c0000000-cfffffff ioport:f000(size=256) memory:feb00000-feb3ffff memory:c0000-dffff -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1863390 Title: GPU lockup ring 0 stalled for more than X msec To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/1863390/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs