On Fri, Sep 30, 2011 at 9:41 PM, Robert Watson wrote: > > On Wed, 28 Sep 2011, Mikolaj Golub wrote: > >> On Mon, 26 Sep 2011 16:12:55 +0200 K. Macy wrote: >> >> KM> Sorry, didn't look at the images (limited bw), I've seen something KM> >> like this before in timewait. This "can't happen" with UDP so will be KM> >> interested in learning more about the bug. >> >> The panic can be easily triggered by this: > > Hi: > > Just catching up on this thread. I think the analysis here is generally > right: in 9.0, you're much more likely to see an inpcb with its in_socket > pointer cleared in the hash list than in prior releases, and > in_pcbbind_setup() trips over this. > > However, at least on first glance (and from the perspective of invariants > here), I think the bug is actualy that in_pcbbind_setup() is asking > in_pcblookup_local() for an inpcb and then access the returned inpcb's > in_socket pointer without acquiring a lock on the inpcb. Structurally, it > can't acquire this lock for lock order reasons -- it already holds the lock > on its own inpcb. Therefore, we should only access fields that are safe to > follow in an inpcb when you hold a reference via the hash lock and not a > lock on the inpcb itself, which appears generally OK (+/-) for all the > fields in that clause but the t->inp_socket->so_options dereference. > > A preferred fix would cache the SO_REUSEPORT flag in an inpcb-layer field, > such as inp_flags2, giving us access to its value without having to walk > into the attached (or not) socket. > > This raises another structural question, which is whether we need a new > inp_foo flags field that is protected explicitly by the hash lock, and not > by the inpcb lock, which could hold fields relevant to address binding. I > don't think we need to solve that problem in this context, as a slightly > race on SO_REUSEPORT is likely acceptable. > > The suggested fix does perform the desired function of explicitly detaching > the inpcb from the hash list before the socket is disconnected from the > inpcb. However, it's incomplete in that the invariant that's being broken is > also relied on for other protocols (such as raw sockets). The correct > invariant is that inp_socket is safe to follow unconditionally if an inpcb > is locked and INP_DROPPED isn't set -- the bug is in "locked" not in > "INP_DROPPED", which is why I think this is the wrong fix, even though it > prevents a panic :-).
Hello Robert, Thank you for taking your valuable time to find out the problem. Since I don't have idea about network internals, would you have a patch about this? I'd be glad to test it, thanks again. > Robert Best regards, Dave. _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
