[ 918.1424782] panic: kernel diagnostic assertion "(ctx->wwx_class == mutex->wwm_u.ctx->wwx_class)" failed: file "/usr/src/sys/external/bsd/drm2/linux/linux_ww_mutex.c", line 401 ww mutex class mismatch: 0xffffffff81abbf80 != 0xffff84e9edb82808
[ 918.1624783] cpu2: Begin traceback...
[ 918.1624783] vpanic() at netbsd:vpanic+0x183
[ 918.1724773] kern_assert() at netbsd:kern_assert+0x4b
[ 918.1724773] ww_mutex_lock_wait_sig() at netbsd:ww_mutex_lock_wait_sig+0x235
[ 918.1824805] linux_ww_mutex_lock_slow_interruptible() at netbsd:linux_ww_mutex_lock_slow_interruptible+0x160
[ 918.1924769] ttm_eu_reserve_buffers() at netbsd:ttm_eu_reserve_buffers+0x103
[ 918.2024768] radeon_bo_list_validate() at netbsd:radeon_bo_list_validate+0xa4
[ 918.2124766] radeon_cs_ioctl() at netbsd:radeon_cs_ioctl+0x3fa
[ 918.2124766] drm_ioctl() at netbsd:drm_ioctl+0x23d
[ 918.2224770] drm_ioctl_shim() at netbsd:drm_ioctl_shim+0x37
[ 918.2224770] sys_ioctl() at netbsd:sys_ioctl+0x56d
[ 918.2324768] syscall() at netbsd:syscall+0x196

code is:

390 static int
391 ww_mutex_lock_wait_sig(struct ww_mutex *mutex, struct ww_acquire_ctx *ctx)
392 {
[ ... ]
401         KASSERTMSG((ctx->wwx_class == mutex->wwm_u.ctx->wwx_class),
402             "ww mutex class mismatch: %p != %p",
403             ctx->wwx_class, mutex->wwm_u.ctx->wwx_class);

caller is:

 85 int ttm_eu_reserve_buffers(struct ww_acquire_ctx *ticket,
[ .. ]
124                 ttm_eu_backoff_reservation_reverse(list, entry);
125
126                 if (ret == -EDEADLK) {
127                         if (intr) {
128                                 ret = dma_resv_lock_slow_interruptible(bo->base.resv,
129                                                                                  ticket);

where dma_resv_lock_slow_interruptible() is a frontend to
ww_mutex_lock_slow_interruptible().