Date: Mon, 11 Aug 2003 18:03:15 -0400 (EDT) From: John Baldwin <jhb@FreeBSD.org> To: Ted Unangst <tedu@stanford.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: possible deadlocks? Message-ID: <XFMail.20030811180315.jhb@FreeBSD.org> In-Reply-To: <Pine.GSO.4.44.0308111434150.19330-100000@saga8.Stanford.EDU>
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On 11-Aug-2003 Ted Unangst wrote: > one more. This falls into the very improbable category. Ordinarily, I > don't think this is possible because FreeBSD doesn't support hotplug PCI, > so sk attachment can't be raced. > > However, assuming I had some hot plug sk card, it seems like running > ifconfig sk0 at just the wrong point during sk1 attach will deadlock. If > it absolutely can not happen (for a reason other than sk is attached > before init runs) please explain. > > sk.c: > sk_attach_xmac() > SK_LOCK(sc); /* grabs */ > ether_ifattach() > ifattach() > IFNET_WLOCK() /* waits for 2 */ > > in6_ifattach.c: > in6_nigroup_attach() > IFNET_RLOCK() /* grabs */ > in6_addmulti() > if_addmulti() > sk_ioctl() > SK_IF_LOCK(); /* waits for 1 */ You can't ifconfig sk0 until after it attaches. sk0 and sk1 don't share locks, so you don't have to worry about the interaction there. Also, SK_LOCK != SK_IF_LOCK, or is that a typo? If it is a typo, then the lock order should still be fixed in some fashion. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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