Re: port-alpha/53809: kernel locks up

[Jason Thorpe <thorpej%me.com@localhost>]

The following reply was made to PR port-alpha/53809; it has been noted by GNATS.

From: Jason Thorpe <thorpej%me.com@localhost>
To: "gnats-bugs%netbsd.org@localhost" <gnats-bugs%NetBSD.org@localhost>
Cc: port-alpha-maintainer%netbsd.org@localhost,
 gnats-admin%netbsd.org@localhost,
 netbsd-bugs%netbsd.org@localhost,
 "martin%netbsd.org@localhost" <martin%NetBSD.org@localhost>
Subject: Re: port-alpha/53809: kernel locks up
Date: Wed, 2 Jan 2019 09:31:49 -0800

 > On Jan 2, 2019, at 1:30 AM, Martin Husemann <martin%duskware.de@localhost> =
 wrote:
 >=20
 > The following reply was made to PR port-alpha/53809; it has been noted =
 by GNATS.
 >=20
 > From: Martin Husemann <martin%duskware.de@localhost>
 > To: gnats-bugs%NetBSD.org@localhost
 > Cc:=20
 > Subject: Re: port-alpha/53809: kernel locks up
 > Date: Wed, 2 Jan 2019 10:29:30 +0100
 >=20
 > Another DIAGNOSTIC hit:
 >=20
 > [ 2741.2335401] Using reserved ASN! (line 2135)
 > [ 2741.2335401] panic: PMAP_ACTIVATE_ASN_SANITY
 > [ 2741.2335401] cpu0: Begin traceback...
 > [ 2741.2335401] alpha trace requires known PC =3Deject=3D
 > [ 2741.2335401] cpu0: End traceback...
 > [ 2741.2335401] cpu1: shutting down...
 
 Hm... A call to pmap_asn_alloc() immediately precedes the call to =
 PMAP_ACTIVATE() on line 2135, and one should never come out of there =
 with PMAP_ASN_RESERVED, unless the pmap is referencing the =
 kernel_lev1map.  The the sanity check fails because the pmap is NOT =
 referencing kernel_lev1map, but the pmap's ASN info for the current CPU =
 has PMAP_ASN_RESERVED assigned.
 
 Any process that's running user code should never be referencing =
 kernel_lev1map, so I'm having a hard time seeing how two threads could =
 be racing here (the pmap is not locked in pmap_activate()).  Though, =
 maybe there's some case I'm not thinking of.  I'll build you a GENERIC =
 kernel with a change to lock the pmap across pmap_activate(), and also =
 to disable the problematic test in pmap_emulate_reference().
 
 Stay tuned
 
 >=20
 > Guess I should stop trying DEBUG :-/
 >=20
 > Martin
 >=20
 
 -- thorpej