Date: Fri, 7 Oct 2011 09:12:36 +0800 From: dave jones <s.dave.jones@gmail.com> To: Mikolaj Golub <trociny@freebsd.org> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Adrian Chadd <adrian@freebsd.org>, Robert Watson <rwatson@freebsd.org>, "K. Macy" <kmacy@freebsd.org>, Arnaud Lacombe <lacombar@gmail.com> Subject: Re: Kernel panic on FreeBSD 9.0-beta2 Message-ID: <CANf5e8YtQ5P2euF7E-D6Wt7U38UuLc8KVU-NCehq74XV_WTvBg@mail.gmail.com> In-Reply-To: <86y5x0ooik.fsf@in138.ua3> References: <CANf5e8aG4go4M_vsRExUsJB_sjaN5x-QK-TCDAhSH64JSo0mdQ@mail.gmail.com> <CACqU3MXStMMEoppvDtZS6hV4WGttbdJiF8E-ORwJ%2BQSmnTy-Yg@mail.gmail.com> <CACqU3MV-t4Va6VWUoXy1Y9FYnNJTUw1X%2BE7ik-2%2BtMVuVOV3RA@mail.gmail.com> <CAJ-Vmom-177OkdUXjz%2BZLqbaqn=p%2BuTGypiVuMqdeXgdOgb4hQ@mail.gmail.com> <CAHM0Q_Mmn3z1V6AtZHQMpgbdY7oQqOChiNt=8NJrZQDnravb7A@mail.gmail.com> <CACqU3MU9ZZtOsdBOa%2BF3SqUaYgO%2BEo0v1ACjY0S4rY4fRQyv5Q@mail.gmail.com> <CAHM0Q_PZD9_0ZkELZ5XL8Ebh8eD-uFuSjXWKKVpGDeM_JDaqMA@mail.gmail.com> <8662kcigif.fsf@kopusha.home.net> <alpine.BSF.2.00.1109301432570.65269@fledge.watson.org> <CANf5e8ab=mUw-AJuRXZy1T6%2BZcryxjKfuCOsakPPfqatuA3HdA@mail.gmail.com> <86y5x0ooik.fsf@in138.ua3>
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2011/10/4 Mikolaj Golub : > > On Sat, 1 Oct 2011 14:15:45 +0800 dave jones wrote: > > =A0dj> On Fri, Sep 30, 2011 at 9:41 PM, Robert Watson wrote: > =A0>> > =A0>> On Wed, 28 Sep 2011, Mikolaj Golub wrote: > =A0>> > =A0>>> On Mon, 26 Sep 2011 16:12:55 +0200 K. Macy wrote: > =A0>>> > =A0>>> KM> Sorry, didn't look at the images (limited bw), I've seen somet= hing KM> > =A0>>> like this before in timewait. This "can't happen" with UDP so will= be KM> > =A0>>> interested in learning more about the bug. > =A0>>> > =A0>>> The panic can be easily triggered by this: > =A0>> > =A0>> Hi: > =A0>> > =A0>> Just catching up on this thread. =A0I think the analysis here is ge= nerally > =A0>> right: in 9.0, you're much more likely to see an inpcb with its in_= socket > =A0>> pointer cleared in the hash list than in prior releases, and > =A0>> in_pcbbind_setup() trips over this. > =A0>> > =A0>> However, at least on first glance (and from the perspective of inva= riants > =A0>> here), I think the bug is actualy that in_pcbbind_setup() is asking > =A0>> in_pcblookup_local() for an inpcb and then access the returned inpc= b's > =A0>> in_socket pointer without acquiring a lock on the inpcb. =A0Structu= rally, it > =A0>> can't acquire this lock for lock order reasons -- it already holds = the lock > =A0>> on its own inpcb. =A0Therefore, we should only access fields that a= re safe to > =A0>> follow in an inpcb when you hold a reference via the hash lock and = not a > =A0>> lock on the inpcb itself, which appears generally OK (+/-) for all = the > =A0>> fields in that clause but the t->inp_socket->so_options dereference= . > =A0>> > =A0>> A preferred fix would cache the SO_REUSEPORT flag in an inpcb-layer= field, > =A0>> such as inp_flags2, giving us access to its value without having to= walk > =A0>> into the attached (or not) socket. > =A0>> > =A0>> This raises another structural question, which is whether we need a= new > =A0>> inp_foo flags field that is protected explicitly by the hash lock, = and not > =A0>> by the inpcb lock, which could hold fields relevant to address bind= ing. =A0I > =A0>> don't think we need to solve that problem in this context, as a sli= ghtly > =A0>> race on SO_REUSEPORT is likely acceptable. > =A0>> > =A0>> The suggested fix does perform the desired function of explicitly d= etaching > =A0>> the inpcb from the hash list before the socket is disconnected from= the > =A0>> inpcb. However, it's incomplete in that the invariant that's being = broken is > =A0>> also relied on for other protocols (such as raw sockets). =A0The co= rrect > =A0>> invariant is that inp_socket is safe to follow unconditionally if a= n inpcb > =A0>> is locked and INP_DROPPED isn't set -- the bug is in "locked" not i= n > =A0>> "INP_DROPPED", which is why I think this is the wrong fix, even tho= ugh it > =A0>> prevents a panic :-). > > =A0dj> Hello Robert, > > =A0dj> Thank you for taking your valuable time to find out the problem. > =A0dj> Since I don't have idea about network internals, would you have a = patch > =A0dj> about this? I'd be glad to test it, thanks again. > > Here is the patch that implements what Robert suggests. > > Dave, could you test it? Sure. Thanks for cooking the patch. Machines have been running two days now without panic. > -- > Mikolaj Golub Best regards, Dave.
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