kern/57537: radeon drm hangs with multiple glxgears active

[mrg%eterna.com.au@localhost]

>Number:         57537
>Category:       kern
>Synopsis:       radeon drm hangs with multiple glxgears active
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Jul 22 06:45:00 +0000 2023
>Originator:     matthew green
>Release:        NetBSD 10.99.6 amd64
>Organization:
people's front against (bozotic) www (softwar foundation)
>Environment:

	-10 or -current amd64.

	radeon0 at pci1 dev 0 function 0: ATI Technologies Mobility Radeon HD 4670 (rev. 0x00)
	[ ... ]
	[drm] initializing kernel modesetting (RV730 0x1002:0x9488 0x1028:0x02FE 0x00).
	[ .. normal looking messages, no errors ]

>Description:
	
	on a system with radeon 4760 running 8 concurrent glxgears
	pretty quickly has at least 3-5 of them lock up and stop
	spinning the gear.  (the system has 8 cpu threads.)

	crash(8) shows that each of these glxgears has 3 lwps, two
	are in lwp_park() and for the 5 stuck instances right now,
	this is the kernel stack trace (all the same):

	crash> bt/a ffff8fb035453140
	trace: pid 1159 lid 1972 at 0xffff928243e406f0
	sleepq_block() at sleepq_block+0x166
	cv_wait_sig() at cv_wait_sig+0x55
	ww_mutex_lock_wait_sig() at ww_mutex_lock_wait_sig+0xab
	linux_ww_mutex_lock_interruptible() at linux_ww_mutex_lock_interruptible+0x1d3
	ttm_eu_reserve_buffers() at ttm_eu_reserve_buffers+0x1a6
	radeon_bo_list_validate() at radeon_bo_list_validate+0xab
	radeon_cs_ioctl() at radeon_cs_ioctl+0x975
	drm_ioctl() at drm_ioctl+0x260
	drm_ioctl_shim() at drm_ioctl_shim+0x45
	sys_ioctl() at sys_ioctl+0x5d3
	syscall() at syscall+0x1ae
	--- syscall (number 54) ---
	syscall+0x1ae:

>How-To-Repeat:

	boot on r600 system, run concurrent glxgears with
	"vblank_mode=1" in the environment.

>Fix: