Re: [BETA7-panic] sodealloc(): so_count 1

On Mon, 11 Oct 2004, Vlad wrote:

> this patch is a replacement (not addition) to what Brian came up with
> before here http://green.homeunix.org/~green/tcp_accept_race_crash.patch
> correct? 
> 
> I see they patch different files, so just making sure
> 
> thank you guys for your work and patience with the problem :) 

This is a replacement patch.  Brian explored solutions to some more broad
potential problems, but we concluded the risks were a bit high for more
broad changes this close to the release.  This patch is hoped to correct
the specific class of problems you were seeing.  I talked with Brian some
about my more broad plans for cleaning up socket state issues, which will
be in the pipeline for 5.4. 

Thanks!

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert_at_fledge.watson.org      Principal Research Scientist, McAfee Research


> 
> 
> On Mon, 11 Oct 2004 04:13:15 -0400 (EDT), Robert Watson
> <rwatson_at_freebsd.org> wrote:
> > 
> > On Sun, 10 Oct 2004, Marc UBM Bocklet wrote:
> > 
> > > No, but I can revert the local patches, configure a dump device and try
> > > getting one tomorrow or the day after that.
> > 
> > Marc,
> > 
> > Afer a couple of days of experimenting and chatting, Brian and I have
> > developed what we hope is a less intrusive but fully functional fix for
> > this problem.  I ran it through a barrage of tests yesterday, although I
> > couldn't reproduce the problem originally, and the system still appears to
> > run :-).  I've committed the patch to CVS HEAD (6.x), and will merge to
> > 5.x in a few days, and assuming that your testing of the change doesn't
> > reveal that it didn't fix the problem.  I have included a copy of the
> > patch committed (minus $FreeBSD$ change) below.
> > 
> > If you could give this a spin, it would be much appreciated.  Thanks for
> > your (and Vlad's) patience as we worked this out!  (And many thanks to
> > Brian for doing so much of the work to fix it).
> > 
> > Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
> > robert_at_fledge.watson.org      Principal Research Scientist, McAfee Research
> > 
> > 
> > Index: uipc_socket.c
> > ===================================================================
> > RCS file: /home/ncvs/src/sys/kern/uipc_socket.c,v
> > retrieving revision 1.212
> > retrieving revision 1.213
> > diff -u -r1.212 -r1.213
> > --- uipc_socket.c       5 Sep 2004 14:33:21 -0000       1.212
> > +++ uipc_socket.c       11 Oct 2004 08:11:26 -0000      1.213
> > _at__at_ -316,22 +316,34 _at__at_
> >        return (0);
> > }
> > 
> > +/*
> > + * Attempt to free a socket.  This should really be sotryfree().
> > + *
> > + * We free the socket if the protocol is no longer interested in the socket,
> > + * there's no file descriptor reference, and the refcount is 0.  While the
> > + * calling macro sotryfree() tests the refcount, sofree() has to test it
> > + * again as it's possible to race with an accept()ing thread if the socket is
> > + * in an listen queue of a listen socket, as being in the listen queue
> > + * doesn't elevate the reference count.  sofree() acquires the accept mutex
> > + * early for this test in order to avoid that race.
> > + */
> > void
> > sofree(so)
> >        struct socket *so;
> > {
> >        struct socket *head;
> > 
> > -       KASSERT(so->so_count == 0, ("socket %p so_count not 0", so));
> > -       SOCK_LOCK_ASSERT(so);
> > +       SOCK_UNLOCK(so);
> > +       ACCEPT_LOCK();
> > +       SOCK_LOCK(so);
> > 
> > -       if (so->so_pcb != NULL || (so->so_state & SS_NOFDREF) == 0) {
> > +       if (so->so_pcb != NULL || (so->so_state & SS_NOFDREF) == 0 ||
> > +           so->so_count != 0) {
> >                SOCK_UNLOCK(so);
> > +               ACCEPT_UNLOCK();
> >                return;
> >        }
> > 
> > -       SOCK_UNLOCK(so);
> > -       ACCEPT_LOCK();
> >        head = so->so_head;
> >        if (head != NULL) {
> >                KASSERT((so->so_qstate & SQ_COMP) != 0 ||
> > _at__at_ -353,6 +365,7 _at__at_
> >                 * the listening socket is closed.
> >                 */
> >                if ((so->so_qstate & SQ_COMP) != 0) {
> > +                       SOCK_UNLOCK(so);
> >                        ACCEPT_UNLOCK();
> >                        return;
> >                }
> > _at__at_ -365,6 +378,7 _at__at_
> >            (so->so_qstate & SQ_INCOMP) == 0,
> >            ("sofree: so_head == NULL, but still SQ_COMP(%d) or SQ_INCOMP(%d)",
> >            so->so_qstate & SQ_COMP, so->so_qstate & SQ_INCOMP));
> > +       SOCK_UNLOCK(so);
> >        ACCEPT_UNLOCK();
> >        SOCKBUF_LOCK(&so->so_snd);
> >        so->so_snd.sb_flags |= SB_NOINTR;
> > 
> > 
> > 
> > 
> > _______________________________________________
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> > 
> 
> 
> -- 
> 
> Vlad
>