Re: rev. 1.94 of netinet/in.c broke CARP

From: Robert Watson <rwatson@xxxxxxxxxxx>
Date: Thu, 25 Jan 2007 22:00:08 +0000 (GMT)

On Fri, 26 Jan 2007, Gleb Smirnoff wrote:

On Thu, Jan 25, 2007 at 08:40:52PM +0000, Robert Watson wrote:
R> Architecturally, the right fix is that CARP needs to have a handler for
R> ifnet destruction that always runs before the multicast address garbage
R> collection. I'm pretty preoccupied for the next few days due to an
R> impending paper deadline, so can't investigate further currently, but one
R> way or the other that ordering dependency needs to be expressed. If done
R> properly, CARP will always have released its multicast address before they
R> are forceably removed. Having the reference count is good too, but what I
R> describe should be sufficient regardless of the refcount.

This means removing usage of EVENTHANDLER(9) and going back to exporting carp_ifdetach() and calling it directly from if_detach(). This is back out revision 1.255 of net/if.c. Not sure what is a right way...

I am worried about that CARP is not the only subsystem in kernel that can join a multicast group on an ifnet, and keep a pointer to the multicast instance.

Alternatively, we move to having two event handlers: one for general stack consumers to use, and a second one to do low level address and protocol cleanup. CARP would use the former, multicast address stuff the latter...

Robert N M Watson
Computer Laboratory
University of Cambridge
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Follow-Ups:
- Re: rev. 1.94 of netinet/in.c broke CARP
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References:
- rev. 1.94 of netinet/in.c broke CARP
  - From: Gleb Smirnoff
- Re: rev. 1.94 of netinet/in.c broke CARP
  - From: Bruce M. Simpson
- Re: rev. 1.94 of netinet/in.c broke CARP
  - From: Gleb Smirnoff
- Re: rev. 1.94 of netinet/in.c broke CARP
  - From: Robert Watson
- Re: rev. 1.94 of netinet/in.c broke CARP
  - From: Gleb Smirnoff

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Relevant Pages

Re: rev. 1.94 of netinet/in.c broke CARP
... the right fix is that CARP needs to have a handler for ... R> ifnet destruction
that always runs before the multicast address garbage ... CARP will always have released
its multicast address before they ... (freebsd-net)
Re: rev. 1.94 of netinet/in.c broke CARP
... The real fix for netinet is to do what netinet6 does; that is, refcount the memberships
and keep them in a list, rather than a vector. ... Unfortunately, due to how CARP works,
two bugs were fixed at the expense of introducing another. ... Call multicast cleanup,
if we are destroying carp interface itself. ... Resource allocation and free for CARP runs along
two separate paths; the case where a member interface is detached cannot be considered the same as when
CARP itself is detaching, ... (freebsd-net)
rev. 1.94 of netinet/in.c broke CARP
... that revision 1.94 of in.c has broke CARP. ... of all multicast instances
and deletes all the instances, ... ifconfig vlan0 destroy ... (freebsd-net)
Re: rev. 1.94 of netinet/in.c broke CARP
... R>>R> ifnet destruction that always runs before the multicast address
garbage ... CARP will always have released its multicast address before ... Is adding
a generic GC function a correct way or was it better to just fix ... (freebsd-net)
Re: rev. 1.94 of netinet/in.c broke CARP
... the right fix is that CARP needs to have a handler ... for R> ifnet destruction
that always runs before the multicast address ... its multicast address before they R>
are forceably removed. ... (freebsd-net)