Possible UDP deadlock/panic fix

[Robert Watson]

On Tue, 23 Sep 2008, Mario Sergio Fujikawa Ferreira wrote:

>    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.

I've now merged the fix to stable/7, thanks to both of you for reporting the 
problem.

Robert N M Watson
Computer Laboratory
University of Cambridge

>
>    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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>
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