port-pmax/55715: pmax testbed panics with "assertion "asid == curcpu()->ci_pmap_asid_cur" failed"

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         55715
>Category:       port-pmax
>Synopsis:       pmax testbed panics with "assertion "asid == curcpu()->ci_pmap_asid_cur" failed"
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    port-pmax-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Oct 11 14:55:00 +0000 2020
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:
>Environment:
System: NetBSD
Architecture: mips
Machine: pmax
>Description:

The TNF NetBSD/pmax testbed consistently panics during the
sigbus_adraln test case of the lib/libc/gen/t_siginfo test:

  lib/libc/gen/t_siginfo (178/885): 8 test cases
      sigalarm: [1.164062s] Passed.
      sigbus_adraln: [ 5559.7773467] trap: pid 2983(t_siginfo): sig 10: cause=0x10 epc=0xd7b1010 va=0x7b6dc011
  [ 5559.7773467] registers:
  [ 5559.7773467] [ 0]=00000000 [ 1]=ffffffe0 [ 2]=7b6dc011 [ 3]=00003fce
  [ 5559.7773467] [ 4]=7b6846f8 [ 5]=00000001 [ 6]=00000001 [ 7]=7b3d0031
  [ 5559.7773467] [ 8]=00000002 [ 9]=00000002 [10]=fffffff6 [11]=0000000a
  [ 5559.7773467] [12]=00000001 [13]=7ff16360 [14]=7b6a6008 [15]=00000001
  [ 5559.7773467] [16]=0d7c3c34 [17]=0d7c3c88 [18]=7ff16c78 [19]=00000010
  [ 5559.7773467] [20]=7ff16c60 [21]=00000001 [22]=7b683004 [23]=7b6d0000
  [ 5559.7773467] [24]=7b6a63b0 [25]=7b620488 [26]=00000000 [27]=00000000
  [ 5559.7773467] [28]=0d7cbaf0 [29]=7ff16b98 [30]=7b6c0000 [31]=0d7b1008
  [ 5559.7929717] panic: kernel debugging assertion "asid == curcpu()->ci_pmap_asid_cur" failed: file "/tmp/bracket/build/2020.10.11.07.08.29-pmax/src/sys/uvm/pmap/pmap_tlb.c", line 1077 pmap_tlb_asid_check: asid (0) != current asid (0xd)
  [ 5559.7929717] cpu0: Begin traceback...
  kernel debugging assertion "asid == curcpu()->ci_pmap_asid_cur" failed:[ 5559.7929717] pid -2135851832 not found
  [ 5559.7929717] cpu0: End traceback...
  [ 5559.7929717] 0x80b17cb0: cpu_reboot+3c (80b16000,0,829d4400,8056ba80) ra 802f9d4c sz 24
  [ 5559.7929717] 0x80b17cc8: kern_reboot+7c (80b16000,0,829d4400,8056ba80) ra 80342890 sz 40
  [ 5559.7929717] 0x80b17cf0: vpanic+1b0 (80b16000,0,829d4400,8056ba80) ra 8047e8cc sz 48
  [ 5559.7929717] 0x80b17d20: kern_assert+3c (80b16000,804a8afc,804a8ad8,804a88c0) ra 80051268 sz 32
  [ 5559.7929717] 0x80b17d40: pmap_tlb_asid_check+84 (80b16000,804a8afc,804a8ad8,804a88c0) ra 80052f50 sz 40
  [ 5559.7929717] 0x80b17d68: trap+acc (80b16000,804a8afc,804a8ad8,7b620148) ra 80043fd4 sz 480
  [ 5559.7929717] 0x80b17f48: mips1_user_gen_exception+e4 (80b16000,804a8afc,804a8ad8,7b620148) ra 0 sz 0
  [ 5559.7929717] User-level: pid 2983.2983

  [ 5559.7929717] dump to dev 19,1 not possible
  [ 5559.7929717] rebooting...

The problem started some time between source dates 2020.07.23.12.13.25
and 2020.09.01.04.19.16.

Console log:

  http://releng.netbsd.org/b5reports/pmax/2020/2020.09.01.04.19.16/test.log

>How-To-Repeat:

>Fix: