Date: Fri, 4 Nov 2005 07:52:29 -0500 From: John Baldwin <jhb@FreeBSD.org> To: arch@FreeBSD.org Subject: ether_ifdetach() races round 3(?) Message-ID: <200511040752.29724.jhb@FreeBSD.org>
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I had another moment of inspiration regarding the ether_ifdetach() races=20
during my shower this morning. Maybe this will gives us a viable solution=
=20
this time.
The reason we are having races is that once we call foo_stop(), the driver=
=20
state is out of sync with the ifnet state because IFF_UP is still set even=
=20
though the driver effectively has marked the interface down. The obvious=20
solution to that is to have the ifnet code "officially" mark the driver dow=
n=20
by clearing IFF_UP. This would result in foo_ioctl() calling foo_stop()=20
rather than foo_detach() calling it explicitly. I think this is actually=20
cleaner in that drivers already rely on the ifnet layer calling foo_init()=
=20
and don't call foo_init() in foo_attach(). Moving foo_stop() out of=20
foo_detach() and into the ifnet layer would thus be more consistent. =20
foo_detach() would go from:
if (device_is_attached(sc)) {
FOO_LOCK(sc);
foo_stop(sc);
FOO_UNLOCK(sc);
callout_drain(&sc->sc_stat_callout);
ether_ifdetach(sc->sc_ifp);
}
to just:
if (device_is_attached(sc)) {
ether_ifdetach(sc->sc_ifp);
callout_drain(&sc->sc_stat_callout);
}
The only question then is when should ether_ifdetach() mark the interface a=
s=20
down, and this actually ends up nice as it lets us fix all the other races=
=20
with BPF and userland ioctls. Basically, we should detach the ifnet from=20
userland so no more userland requests can come in, then tear down kernel=20
consumers such as BPF, and mark the interface down resulting in an ioctl()=
=20
that clears IFF_UP and calls foo_stop().
=2D-=20
John Baldwin <jhb@FreeBSD.org> =A0<>< =A0http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" =A0=3D =A0http://www.FreeBSD.org
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