cvs commit: src/sys/netinet in_mcast.c ip_divert.c
Christian S.J. Peron
csjp at FreeBSD.org
Mon Aug 6 15:06:37 PDT 2007
csjp 2007-08-06 22:06:36 UTC
FreeBSD src repository
sys/netinet in_mcast.c ip_divert.c
Over the past couple of years, there have been a number of reports relating
the use of divert sockets to dead locks. A number of LORs have been reported
between divert and a number of other network subsystems including: IPSEC, Pfil,
multicast, ipfw and others. Other dead locks could occur because of recursive
entry into the IP stack. This change should take care of most if not all of
A summary of the changes follow:
- We disallow multicast operations on divert sockets. It really doesn't make
semantic sense to allow this, since typically you would set multicast
parameters on multicast end points.
NOTE: As a part of this change, we actually dis-allow multicast options on
any socket that IS a divert socket OR IS NOT a SOCK_RAW or SOCK_DGRAM family
- We check to see if there are any socket options that have been specified on
the socket, and if there was (which is very un-common and also probably
doesnt make sense to support) we duplicate the mbuf carrying the options.
- We then drop the INP/INFO locks over the call to ip_output(). It should be
noted that since we no longer support multicast operations on divert sockets
and we have duplicated any socket options, we no longer need the reference
to the pcb to be coherent.
- Finally, we replaced the call to ip_input() to use netisr queuing. This
should remove the recursive entry into the IP stack from divert.
By dropping the locks over the call to ip_output() we eliminate all the lock
ordering issues above. By switching over to netisr on the inbound path,
we can no longer recursively enter the ip_input() code via divert.
I have tested this change by using the following command:
ipfwpcap -r 8000 - | tcpdump -r - -nn -v
This should exercise the input and re-injection (outbound) path, which is
very similar to the work load performed by natd(8). Additionally, I have
run some ospf daemons which have a heavy reliance on raw sockets and
Approved by: re@ (kensmith)
MFC after: 1 month
Discussed with: julian, andre et al (on freebsd-net)
In collaboration with: bms , rwatson 
 bms helped out with the multicast decisions
 rwatson submitted the original netisr patches and came up with some
of the original ideas on how to combat this issue.
Revision Changes Path
1.3 +21 -0 src/sys/netinet/in_mcast.c
1.129 +45 -10 src/sys/netinet/ip_divert.c
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