From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yoann Padioleau <pad@fb.com>
To: Yoann Padioleau <pad@fb.com>
Date: Sun, 22 Jun 2014 22:25:29 +0000
Message-ID: <1AE8E693-C840-4E40-BB19-6DF52A98E578@fb.com>
References: <EC073287-823A-4F0C-ACFD-2831DE775D53@fb.com>
In-Reply-To: <EC073287-823A-4F0C-ACFD-2831DE775D53@fb.com>
Content-Type: text/plain; charset="us-ascii"
Content-ID: <568A5A1CE9C143428192EFF8A56BEFDC@fb.com>
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Cc: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: Re: [9fans] bug in procwired() for x86 scheduler?
Topicbox-Message-UUID: fc8e88ce-ead8-11e9-9d60-3106f5b1d025

The code should be

if(up !=3D p && (p->wired =3D=3D nil || p->wired =3D=3D MACHP(m->machno))
   m->readied =3D p;

no?

>=20
> if(up !=3D p && (p->wired =3D=3D nil || p->wired =3D=3D m))
> 		m->readied =3D p;	/* group scheduling */

On Jun 22, 2014, at 10:20 AM, yoann padioleau <pad@fb.com> wrote:

> Hi,
>=20
> Looking at the scheduler code I think I've found a bug related to the
> customized affinity one can set for a process.
>=20
> In ready() there is:
>=20
> 	if(up !=3D p && (p->wired =3D=3D nil || p->wired =3D=3D m))
> 		m->readied =3D p;	/* group scheduling */
>=20
> but on x86 'm' is actually set to a fixed address, MACHADDR. Each cpu act=
ually
> have a different mapping in its pagetable to then translate MACHADDR virt=
ual address to a different
> physical address.
>=20
> in procwired() there is:
> 	p->wired =3D MACHP(bm);
>=20
> MACHP is an array of addresses of all Mach in memory but not using this
> MACHADDR fixed virtual address. Each entry corresponds to a different Mac=
h virtual
> address.=20
>=20
> So there is no way the test in ready() p->wired =3D=3D m can even return =
true.=20
>=20