Random screen lockup with hardware acceleration in 16.04

[Ambrose Li]

Since about a week ago, X started locking up randomly (about twice a day). I don’t know what kind of details are relevant but here are some observations:

- When it locks up the screen is always garbled.

- The keyboard would initially work, but if I don’t kill X or reboot right away the keyboard would also stop working after a short time, at which point the system would appear to be locked up hard.

- However, ssh would still work.

- Within the ssh session, any action on the framebuffer would hang. For example, chvt would hang (but can still be suspended).

- Sometimes Xorg can be killed. If Xorg is killed the screen (and keyboard) would appear to return to normal.

- The lockups started around the time hardware acceleration started working on my hardware (NVidia GeForce 9400M) so the problem seems to be related to hardware acceleration.

- The number of simultaneous hardware-accelerated apps using the framebuffer seems to determine whether a lockup will occur. For example, playing the same hardware-accelerated game (in Chrome) would eventually cause an lockup, but playing the same game in only one Chrome window seems to be safe.

- Before a lockup happens, messages similar to the following would appear on the tty where the hardware-accelerated app (e.g., Chrome) is started:

nouveau: 0x20391200
nouveau: 0x00087080
nouveau: 0x00000000
nouveau: 0x203912cf
nouveau: 0x000c6910
nouveau: 0x20000034
nouveau: 0x00000000
nouveau: 0x20391224
nouveau: 0x00087088
nouveau: 0x00000000
nouveau: 0x203912cf
nouveau: 0x000475dc
nouveau: 0x00000004
nouveau: 0x000475ec
nouveau: 0x00000006
nouveau: 0x000375f0
nouveau: 0x00000003
nouveau: ch4: psh 0000000c 0000000d00 0000000d0c
nouveau: 0x00020000
nouveau: 0x00000003
nouveau: 0x00010003
nouveau: ch4: psh 00000000 000006945c 0000069480
nouveau: 0x000475ec
nouveau: 0x00000000
nouveau: 0x000475e0
nouveau: 0x00000000
nouveau: 0x00107b00
nouveau: 0x00000000
nouveau: 0x20217000
nouveau: 0x002f32a4
nouveau: 0x1000f010

This might be the same bug as Bug #1675777, but the symptoms seem to be slightly different:

- In Bug #1675777 the "nouveau" log messages appear in the system log, but in my case it appears on the terminal.
- Also, Bug #1675777 is filed against Ubuntu 17.04, but this is on an Ubuntu 16.04.2 LTS.