Date: Mon, 28 Apr 2003 21:34:02 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: hsu@freebsd.org Cc: current@freebsd.org Subject: Re: panic: sleeping thread owns a mutex Message-ID: <20030428.213402.99254294.imp@bsdimp.com> In-Reply-To: <20030428.205301.112263174.imp@bsdimp.com> References: <imp@bsdimp.com> <0HE200DATX6MIM@mta5.snfc21.pbi.net> <20030428.205301.112263174.imp@bsdimp.com>
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In message: <20030428.205301.112263174.imp@bsdimp.com>
"M. Warner Losh" <imp@bsdimp.com> writes:
: In message: <0HE200DATX6MIM@mta5.snfc21.pbi.net>
: Jeffrey Hsu <hsu@FreeBSD.org> writes:
: : Now, what about the race between the WI_UNLOCK() and the mtx_destroy() in
: : wi_detach() and any other WI_LOCK(), say in wi_start()?
:
: Nothing that I can see. Maybe we need to take out the if lock before
: taking out the wi_lock and require that the if_detach interface be
: locked... But I haven't thought about it too much so there's likely
: issues with it.
Hmmmm, sounds like:
foo_detach(device_t dev)
{
sc = device_get_softc(dev);
if_lock(sc->ifp); // if)lock not exported now
FOO_LOCK(sc);
sc->dead = 1;
// stuff
FOO_UNLOCK(sc);
[1] ifmedia_removeall(&sc->sc_media);
ieee80211_ifdetach(sc->ifp); // NOTE: ifdetach called with
ifp locked, would be required.
bus_teardown_intr(..);
[2] wi_free(dev);
#if __FreeBSD_version >= 500000
mtx_destroy(&sc->sc_mtx);
#endif
}
We have the foo_intr race between [1] and [2], but that's taken care
of with dead. wi_start is called from the network output routines,
potentially, so I think that taking out the interface lock will be the
right thing.
However, this might be a lock order reversal form the init code.
(if_watchdog suffers from this reversal too, potentially). Reversing
the order in foo_detach would not be a good solution, because we'd a
cross-threading locking issue (lock(a), lock(b), unlock(a) is bad).
But I'll freely admit that my understanding of the if_net locking
isn't perfect. :-)
Warner
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