cvs commit: src/sys/dev/re if_re.c

[M. Warner Losh]

In message: <20050916194405.GB24879 at ip.net.ua>
            Ruslan Ermilov <ru at FreeBSD.org> writes:
: On Fri, Sep 16, 2005 at 09:01:40AM -0600, M. Warner Losh wrote:
: > In message: <20050916091928.GG88456 at ip.net.ua>
: >             Ruslan Ermilov <ru at FreeBSD.org> writes:
: > : On Thu, Sep 15, 2005 at 11:56:39PM +0300, Ruslan Ermilov wrote:
: > : > The first is the BPF detach bad interaction with foo_detach(),
: > : > as described in re_detach().  This panic is real with (I think)
: > : > all drivers.  And testing IFF_DRV_RUNNING here doesn't seem to
: > : > be able to prevent the panic.  Perhaps the fix would be to
: > : > move ether_ifdetach() before foo_stop() in foo_detach(), I'm
: > : > not yet sure.
: > : > 
: > : I tried with rl(4) PCCARD, by moving ether_ifdetach() before
: > : rl_stop() in rl_detach().  It fixes the panic when you eject
: > : the card, but doesn't fix it when kldunloading the module.
: > : The difference is that rl_detach() is called already after
: > : miibus0 and rlphy0 has been detached when kldunloading the
: > : module.  When ejecting the card, rl_detach() is called first.
: > : What happens when you kldunload the module with BPF listener
: > : attached, is that bpfdetach() calls rl_ioctl() to reset
: > : promisc, that calls rl_init_locked(), and that results in
: > : 
: > : 	mii = device_get_softc(sc->rl_miibus);
: > : 
: > : being NULL (remember the miibus has already been detached),
: > : and that panics later here:
: > : 
: > : 	mii_mediachg(mii);
: > : 
: > : When we reset IFF_UP, rl_ioctl(SIOCSIFFLAGS) silently exits
: > : and no harm is done.  So the question is: how do we prevent
: > : this from happening without resetting IFF_UP.  One possible
: > : solution would be to add sc->detaching, similar to
: > : sc->suspended, abd check it in rl_ioctl().
: > 
: > Ugg.  In ed, we check to make sure that we still have a child before
: > doing things with mii bus.  A similar fix could be made.
: > 
: No, ed(4) has the same problem:
: 
:         if (sc->miibus != NULL) {
:                 struct mii_data *mii;
:                 mii = device_get_softc(sc->miibus);
:                 mii_mediachg(mii);
:         }
: 

No it doesn't:

void
ed_child_detached(device_t dev, device_t child)
{
	struct ed_softc *sc;

	sc = device_get_softc(dev);
	if (child == sc->miibus)
		sc->miibus = NULL;
}

: The device (sc->miibus) will still be there but already detached,
: and its softc will already be freed, so "mii" will be NULL, and
: mii_mediachg(NULL) will panic the system.

sc->miibus will be NULL after the device is detached, so you don't get
an error.

How again can this happen?

Warner