Date: Mon, 28 Jul 2003 15:38:55 -0700 From: Kris Kennaway <kris@obsecurity.org> To: Kris Kennaway <kris@obsecurity.org> Cc: current@FreeBSD.org Subject: Re: Another LOR with filedesc structure and Giant Message-ID: <20030728223855.GA4834@rot13.obsecurity.org> In-Reply-To: <20030728215312.GA89925@rot13.obsecurity.org> References: <20030727233351.GB80934@rot13.obsecurity.org> <Pine.NEB.3.96L.1030728110437.57321A-100000@fledge.watson.org> <20030728215312.GA89925@rot13.obsecurity.org>
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On Mon, Jul 28, 2003 at 02:53:12PM -0700, Kris Kennaway wrote:
> On Mon, Jul 28, 2003 at 11:09:55AM -0400, Robert Watson wrote:
> >=20
> > On Sun, 27 Jul 2003, Kris Kennaway wrote:
> >=20
> > > After upgrading last night, one of the package machines found this:
> >=20
> > I've bumped into some similar problems -- it's a property of how we
> > current lock select(). We hold the file descriptor lock for the durati=
on
> > of polling each object being "selected", and if any of those objects has
> > to grab a lock for any reason, it has to implicitly fall after the file
> > descriptor lock. I actually run into this in some of our MAC code,
> > because I need to grab a vnode lock to authorize polling the vnode using
> > VOP_POLL(), and since the vnode lock is a sleep lock, this generates a
> > WITNESS warning. Unfortunately, it's not immediately clear what a bett=
er
> > locking scheme would look like without going overboard on the fine-grai=
ned
> > side. We probably need to grab Giant before entering the select code
> > since it's highly likely something in there will require Giant -- it
> > reaches down into VFS, the device stuff, socket code, tc.
>=20
> Also
>=20
> lock order reversal
> 1st 0xc6a69634 filedesc structure (filedesc structure) @ /a/asami/portbu=
ild/i386/src-client/sys/kern/sys_generic.c:1071
> 2nd 0xc04aa120 Giant (Giant) @ /a/asami/portbuild/i386/src-client/sys/fs=
/specfs/spec_vnops.c:372
> Stack backtrace:
> backtrace(c043d4af,c04aa120,c0439aa4,c0439aa4,c0434e3d) at backtrace+0x17
> witness_lock(c04aa120,8,c0434e3d,174,246) at witness_lock+0x672
> _mtx_lock_flags(c04aa120,0,c0434e3d,174,c043daba) at _mtx_lock_flags+0xba
> spec_poll(d8dfcb44,d8dfcb64,c02d119c,d8dfcb44,c04939a0) at spec_poll+0x134
> spec_vnoperate(d8dfcb44,c04939a0,c52cfa44,41,c6cfd280) at spec_vnoperate+=
0x18
> vn_poll(c45dc880,41,c6cfd280,c5f7a4c0,c6cfd280) at vn_poll+0x3c
> pollscan(c5f7a4c0,d8dfcbd4,2,3e7,10) at pollscan+0xb0
> poll(c5f7a4c0,d8dfcd10,c0455899,3ee,3) at poll+0x252
> syscall(2f,2f,2f,0,2) at syscall+0x273
> Xint0x80_syscall() at Xint0x80_syscall+0x1d
#8 0xc0290ed7 in witness_lock (lock=3D0xc04aa120, flags=3D8,
file=3D0xc0434e3d "/a/asami/portbuild/i386/src-client/sys/fs/specfs/spe=
c_vnops.c", line=3D372)
at /a/asami/portbuild/i386/src-client/sys/kern/subr_witness.c:838
#9 0xc0261f4a in _mtx_lock_flags (m=3D0x0, opts=3D0, file=3D0xc04d1818 "",=
line=3D-1068850912)
at /a/asami/portbuild/i386/src-client/sys/kern/kern_mutex.c:334
#10 0xc0231154 in spec_poll (ap=3D0xd8dfcb44)
at /a/asami/portbuild/i386/src-client/sys/fs/specfs/spec_vnops.c:372
#11 0xc0230648 in spec_vnoperate (ap=3D0x0)
at /a/asami/portbuild/i386/src-client/sys/fs/specfs/spec_vnops.c:122
#12 0xc02d119c in vn_poll (fp=3D0x0, events=3D0, active_cred=3D0xc6cfd280, =
td=3D0x0) at vnode_if.h:537
#13 0xc0294c50 in pollscan (td=3D0xc5f7a4c0, fds=3D0xd8dfcbdc, nfd=3D2)
at /a/asami/portbuild/i386/src-client/sys/sys/file.h:272
#14 0xc02948a2 in poll (td=3D0xc5f7a4c0, uap=3D0xd8dfcd10)
at /a/asami/portbuild/i386/src-client/sys/kern/sys_generic.c:1001
#15 0xc03ef9b3 in syscall (frame=3D
{tf_fs =3D 47, tf_es =3D 47, tf_ds =3D 47, tf_edi =3D 0, tf_esi =3D 2=
, tf_ebp =3D -1077940448, tf_isp =3D -656421516, tf_ebx =3D 673224876, tf_e=
dx =3D 139153408, tf_ecx =3D 137314336, tf_eax =3D 209, tf_trapno =3D 0, tf=
_err =3D 2, tf_eip =3D 672942388, tf_cs =3D 31, tf_eflags =3D 659, tf_esp =
=3D -1077940508, tf_ss =3D 47})
at /a/asami/portbuild/i386/src-client/sys/i386/i386/trap.c:1008
#16 0xc03dfbed in Xint0x80_syscall () at {standard input}:144
---Can't read userspace from dump, or kernel process---
Kris
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