Bug 99989

Maybe 30% of the time, the system hangs during boot. There are 2 possible points in the boot sequence where it occurs: Immediately before the login screen appears, or immediately before my desktop is there. I'd love to provide a dmesg log or something, but neither ctrl+alt+Fx nor SysRq keys work anymore if it happens, I have to reset. (How do I get a log from the last boot ?) Behavior of the machine and occasional stack traces I get displayed (but cannot save) suggest to me the problem is graphics drivers related. System is Lubuntu 16.04. I can always boot to command line without problems, and it also never happens afterwards, after it reached the desktop successfully.

lspci -v:

01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV280 [Radeon 9200] (rev 01) (prog-if 00 [VGA controller])
	Subsystem: PC Partner Limited / Sapphire Technology RV280 [Radeon 9200]
	Flags: bus master, 66MHz, medium devsel, latency 32, IRQ 16
	Memory at d8000000 (32-bit, prefetchable) [size=128M]
	I/O ports at c000 [size=256]
	Memory at e9000000 (32-bit, non-prefetchable) [size=64K]
	[virtual] Expansion ROM at e8000000 [disabled] [size=128K]
	Capabilities: [58] AGP version 3.0
	Capabilities: [50] Power Management version 2
	Kernel driver in use: radeon
	Kernel modules: radeonfb, radeon

01:00.1 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] RV280 [Radeon 9200] (Secondary) (rev 01)
	Subsystem: PC Partner Limited / Sapphire Technology RV280 [Radeon 9200] (Secondary)
	Flags: bus master, 66MHz, medium devsel, latency 32
	Memory at e0000000 (32-bit, prefetchable) [size=128M]
	Memory at e9010000 (32-bit, non-prefetchable) [size=64K]
	Capabilities: [50] Power Management version 2