Date: Mon, 12 Aug 2013 08:13:14 -0700 From: David Wolfskill <david@catwhisker.org> To: current@freebsd.org Subject: Early drop to debugger with DEBUG_MEMGUARD Message-ID: <20130812151314.GE1570@albert.catwhisker.org>
next in thread | raw e-mail | index | archive | help
--Uwl7UQhJk99r8jnw
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable
I first noticed this on my laptop on 08 Aug, after having built & booted
FreeBSD 10.0-CURRENT #975 r253985M/253985:1000041: Tue Aug 6 05:28:39 PDT=
2013 root@localhost:/common/S4/obj/usr/src/sys/CANARY i386
OK. I'm away from home, and Internet access is a bit flaky, so
initially, I suspected that something may have gone wrong with my
source update; I later determined that disabling "options DEBUG_MEMGUARD"
would avoid the panic.
That said, I had been running a kernel with DEBUG_MEMGUARD for quite
a while without issues; I suspect that this drop to debugger either
reflects a real problem that disabling DEBUG_MEMGUARD merely hides
or htat the assert in src/sys/kern/subr_vmem.c:1050 isn't actually
correct in all cases.
So I finally(!) had a chance to try to reproduce the error on a
machine with a serial console; here's a cut/paste from that:
=2E..
| 7. Boot [V]erbose: NO | `:` `:`
| | .-- `--.
| | .---.....----.
+-----------------------------------------+
=20
Booting...
GDB: no debug ports present
KDB: debugger backends: ddb
KDB: current backend: ddb
Copyright (c) 1992-2013 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
The Regents of the University of California. All rights reserved.
FreeBSD is a registered trademark of The FreeBSD Foundation.
FreeBSD 10.0-CURRENT #0 r254245M/254246:1000042: Mon Aug 12 07:20:47 PDT 2=
013
root@freebeast.catwhisker.org:/common/S3/obj/usr/src/sys/MEMGUARD i386
FreeBSD clang version 3.3 (tags/RELEASE_33/final 183502) 20130610
WARNING: WITNESS option enabled, expect reduced performance.
panic: Assertion strat =3D=3D M_BESTFIT || strat =3D=3D M_FIRSTFIT failed a=
t /usr/src/sys/kern/subr_vmem.c:1050
cpuid =3D 0
KDB: stack backtrace:
db_trace_self_wrapper(c116fcdc,73752f20,72732f72,79732f63,656b2f73,...) at =
db_trace_self_wrapper+0x2d/frame 0xc1820ba0
kdb_backtrace(c11c4b23,0,c0f8a835,c1820c74,c0f8a835,...) at kdb_backtrace+0=
x30/frame 0xc1820c08
vpanic(c12eea08,100,c0f8a835,c1820c74,c1820c74,...) at vpanic+0x11f/frame 0=
xc1820c44
kassert_panic(c0f8a835,c1172e98,c1172e39,41a,8,...) at kassert_panic+0xea/f=
rame 0xc1820c68
vmem_alloc(c130d680,6681000,2,c1820cc0,3b5,...) at vmem_alloc+0x53/frame 0x=
c1820ca0
memguard_init(c130d680,c0a9fa50,c6800000,20281000,1000,10000,0) at memguard=
_init+0x29/frame 0xc1820cc4
kmeminit(c14b9fd4,c10efc89,0,0,c1820d30,...) at kmeminit+0x171/frame 0xc182=
0cf0
mallocinit(0,0,2,0,c11d3728,...) at mallocinit+0x32/frame 0xc1820d30
mi_startup() at mi_startup+0xf7/frame 0xc1820d58
begin() at begin+0x2c
KDB: enter: panic
[ thread pid 0 tid 0 ]
Stopped at kdb_enter+0x3d: movl $0,kdb_why
db>=20
As you can see, this is well before any device probes or much of
anything else. Thus, I suspect that it's fairly possible that the
assertion may well be OK after a certain point in the boot sequence,
but decidedly *not* OK in this specific instance. Or perhaps the
assertion just doesn't play well with DEBUG_MEMGUARD.
I'm not about to pretend that I have anywhere near enough familiarity
with what's going on to even suggest a fix, but it seems to me that
Something Is Wrong Here.
The kernel config (in this case) is:
include GENERIC
ident MEMGUARD
options DEBUG_MEMGUARD
The system was running a copy of:
FreeBSD 10.0-CURRENT #1243 r254245M/254246:1000042: Mon Aug 12 05:39:42 PD=
T 2013 root@freebeast.catwhisker.org:/common/S4/obj/usr/src/sys/GENERIC=
i386
but with a newly-built MEMGUARD kernel (as above), built from the same
sources.
I have some time to poke at it for the next few hours; subject to
my Internet access & available time, I'm happy to do that, try
patches, or whatever, but I could use a bit of guidance.
Since it's been completely reproducible for me, I suspect that
anyone with sufficiently recenty sources running head can reproduce
it merely by enabling "options DEBUG_MEMGUARD", rebuilding the
kernel, and booting it.
Peace,
david
--=20
David H. Wolfskill david@catwhisker.org
Taliban: Evil men with guns afraid of truth from a 14-year old girl.
See http://www.catwhisker.org/~david/publickey.gpg for my public key.
--Uwl7UQhJk99r8jnw
Content-Type: application/pgp-signature
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.20 (FreeBSD)
iEYEARECAAYFAlII+4kACgkQmprOCmdXAD2NFwCfftEdcQZx8L7KA9TGZTwe9xOI
Z84AoITSeVTZyz7qblPQ6u+qIPB7KYV/
=jYO1
-----END PGP SIGNATURE-----
--Uwl7UQhJk99r8jnw--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20130812151314.GE1570>