Date: Tue, 28 Jun 2016 23:19:45 -0700 From: Matthew Macy <mmacy@nextbsd.org> To: "Julien Charbon" <jch@freebsd.org>, "Randall Stewart" <rrs@netflix.com>, "Hans Petter Selasky" <hselasky@freebsd.org>, "current@freebsd.org" <current@freebsd.org>, "freebsd-net@freebsd.org" <net@freebsd.org> Subject: EBR fix for life cycle races was Re: panic with tcp timers Message-ID: <1559ad03918.b0d7215a52810.5433014980746638496@nextbsd.org> In-Reply-To: <CAHM0Q_OEYhAqqgPj3Zn9z3KNn7c-=B8CLFWR=S7_fU2ePknt7A@mail.gmail.com> References: <20160617045319.GE1076@FreeBSD.org> <1f28844b-b4ea-b544-3892-811f2be327b9@freebsd.org> <20160620073917.GI1076@FreeBSD.org> <1d18d0e2-3e42-cb26-928c-2989d0751884@freebsd.org> <20160620095822.GJ1076@FreeBSD.org> <74bb31b7-a9f5-3d0c-eea0-681872e6f09b@freebsd.org> <18D94615-810E-4E79-A889-4B0CC70F9E45@netflix.com> <6E52CA6A-2153-4EF9-A3E1-97CB0D07EB28@freebsd.org> <ae21858a-e162-6aad-1597-eeff614624c9@freebsd.org> <15598235139.12175f84421756.2471769249719458878@nextbsd.org> <CAHM0Q_OEYhAqqgPj3Zn9z3KNn7c-=B8CLFWR=S7_fU2ePknt7A@mail.gmail.com>
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---- On Tue, 28 Jun 2016 15:51:57 -0700 K. Macy <kmacy@freebsd.org> wrote ---- > On Tue, Jun 28, 2016 at 10:51 AM, Matthew Macy <mmacy@nextbsd.org> wrote: > > You guys should really look at Samy Bahra's epoch based reclamation. I solved a similar problem in drm/linuxkpi using it. > > The point being that this is a bug in the TCP life cycle handling > _not_ in callouts. Churning the callout interface is not the best / > only solution. > -M Please see see D7017/D7018 as an example for an ultimately more robust solution than continued fiddling with the callout interface. https://reviews.freebsd.org/D7018 Cheers. -M > > ---- On Tue, 28 Jun 2016 02:58:56 -0700 Julien Charbon <jch@freebsd.org> wrote ---- > > > > > > Hi Randall, > > > > > > On 6/25/16 4:41 PM, Randall Stewart via freebsd-net wrote: > > > > Ok > > > > > > > > Lets try this again with my source changed to my @freebsd.net :-) > > > > > > > > Now I am also attaching a patch for you Gleb, this will take some poking to > > > > get in to your NF-head since it incorporates some changes we made earlier. > > > > > > > > I think this will fix the problem.. i.e. dealing with two locks in the callout system (which it was > > > > never meant to have done).. > > > > > > > > Note we probably can move the code to use the callout lock init now.. but lets see if this works > > > > on your setup on c096 and if so we can think about doing that. > > > > > > Thanks for proposing a patch. I believe your patch will work with > > > callout lock init, but not without: You still have a use-after-free > > > issue on the tcpcb without callout lock init. > > > > > > The case being subtle as usual, let me try to describe that could happen: > > > > > > With your patch we have: > > > > > > void > > > tcp_timer_keep(void *xtp) > > > { > > > struct tcpcb *tp = xtp; > > > struct tcptemp *t_template; > > > struct inpcb *inp; > > > CURVNET_SET(tp->t_vnet); > > > #ifdef TCPDEBUG > > > int ostate; > > > > > > ostate = tp->t_state; > > > #endif > > > inp = tp->t_inpcb; > > > KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, > > > tp)); > > > INP_WLOCK(inp); > > > if (callout_pending(&tp->t_timers->tt_keep) ### Use after free > > > of tp here > > > !callout_active(&tp->t_timers->tt_keep)) { > > > INP_WUNLOCK(inp); > > > CURVNET_RESTORE(); > > > return; > > > } > > > ... > > > > > > The use-after-free scenario: > > > > > > [CPU 1] the callout fires, tcp_timer_keep entered > > > [CPU 1] blocks on INP_WLOCK(inp); > > > [CPU 2] schedules tcp_timer_keep with callout_reset() > > > [CPU 2] tcp_discardcb called > > > [CPU 2] tcp_timer_keep callout successfully canceled > > > [CPU 2] tcpcb freed > > > [CPU 1] unblocks, the tcpcb is used > > > > > > Then the tcpcb will used just after being freed... Might also crash or > > > not depending in the case. > > > > > > Extra notes: > > > > > > o The invariant I see here is: The "callout successfully canceled" > > > step should never happen when "the callout is currently being executed". > > > > > > o Solutions I see to enforce this invariant: > > > > > > - First solution: Use callout lock init with inp lock, your patch > > > seems to permit that now. > > > > > > - Second solution: Change callout_async_drain() behavior: It can > > > return 0 (fail) when the callout is currently being executed (no matter > > > what). > > > > > > - Third solution: Don't trust callout_async_drain(callout) return > > > value of 1 (success) if the previous call of callout_reset(callout) > > > returned 0 (fail). That was the exact purpose of r284261 change, but > > > this solution is also step backward in modernization of TCP > > > timers/callout... > > > > > > https://svnweb.freebsd.org/base/stable/10/sys/netinet/tcp_timer.c?r1=284261&r2=284260&pathrev=284261 > > > > > > Hopefully my description is clear enough... > > > > > > -- > > > Julien > > > > > > > > > > _______________________________________________ > > freebsd-current@freebsd.org mailing list > > https://lists.freebsd.org/mailman/listinfo/freebsd-current > > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org" > _______________________________________________ > freebsd-current@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org" >
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