Possible UDP deadlock/panic fix

[Mario Sergio Fujikawa Ferreira]

Hi,

     That seems to be working. I've been up and running for 7 hours now 
with your patch.

     The machine is a bit slow but I have both WITNESS and INVARIANTS 
enabled so as to make sure everything is fine.

     Rergads,
         Mario

Robert Watson wrote:
> 
> Attached is an MFC candidate for a patch I just merged to 8.x, which 
> corrects the UDP lock recursion issue both of you were running into.  If 
> it settles well for a couple of days in HEAD then I'll go ahead and 
> request an MFC from re@, but your confirmation as to whether or not this 
> corrects the specific symptoms you are seeing would be very helpful.  I 
> was able to confirm that it eliminated what appeared to be the same 
> problem here when I attempted to reproduce it based on the information 
> you provided, so I'm hopeful.\
> 
> Thanks,
> 
> Robert N M Watson
> Computer Laboratory
> University of Cambridge
> 
> 
> Property changes on: .
> ___________________________________________________________________
> Modified: svn:mergeinfo
>    Merged /head/sys:r183265
> 
> Index: netinet6/udp6_usrreq.c
> ===================================================================
> --- netinet6/udp6_usrreq.c    (revision 183265)
> +++ netinet6/udp6_usrreq.c    (working copy)
> @@ -975,13 +975,23 @@
>                  error = EINVAL;
>                  goto out;
>              }
> +
> +            /*
> +             * XXXRW: We release UDP-layer locks before calling
> +             * udp_send() in order to avoid recursion.  However,
> +             * this does mean there is a short window where inp's
> +             * fields are unstable.  Could this lead to a
> +             * potential race in which the factors causing us to
> +             * select the UDPv4 output routine are invalidated?
> +             */
> +            INP_WUNLOCK(inp);
> +            INP_INFO_WUNLOCK(&udbinfo);
>              if (sin6)
>                  in6_sin6_2_sin_in_sock(addr);
>              pru = inetsw[ip_protox[IPPROTO_UDP]].pr_usrreqs;
> -            error = ((*pru->pru_send)(so, flags, m, addr, control,
> +            /* addr will just be freed in sendit(). */
> +            return ((*pru->pru_send)(so, flags, m, addr, control,
>                  td));
> -            /* addr will just be freed in sendit(). */
> -            goto out;
>          }
>      }
>  #endif
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