On Thursday 30 July 2009 11:39:00 Robert Watson wrote: > On Wed, 29 Jul 2009, Matthew Fleming wrote: > > I'm doing a migration from releng/6.1 to stable/7, and one of the many > > new things is that I get a warning when doing things with ng_socket that > > didn't used to happen. > > > > WARNING: attempt to net_add_domain(netgraph) after domainfinalize() > > I've wondered about these warnings also, and am not sure they're justified > -- any protocol loading after domainfinalize() should expect that timers > are already started, etc, and loadable protocols are clearly desirable. > > > - ignore the warning (usually a bad idea...) > > Probably remove the warning. Some more synchronization is likely required > in domain registration than is currently there -- on the other hand, it's > probably not a big issue that it's missing as write operations on the > domain list are conservative and extremely rare. > > I've CC'd Max Laier, who added the warnings -- perhaps he could lend some > insight into the types of problems he anticipated. The main one I'm aware > of is that mutating the domain list on a live system is risky because it's > not well-synchronized -- however, adding domains should be pretty safe in > practice.
This originated from http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/72772 - if I remember correctly. As usual, the devil is in the details. In the case of the PR there was a race for if_afdata contents. The specific problem described in that PR is a static initialization order problem, but - as I recall - we did see a similar issue with runtime loading of domains as well. The waring was added as a compromise. We didn't want to remove the ability to add netgraph at runtime, but would want to discourage more domains with module capabilities. A full fix was way out of reach at the time as it means a lot of synchronization around otherwise very static data (e.g. if_afdata). Maybe it is time to revisit as we now have read-mostly locks and there is more locking in place for things like address-lists (which was also an area of concern). In any case and my opinion, removing a domain should never be allowed at runtime. Unless we add proper synchronization around the protosw, that is. -- /"\ Best regards, | mla...@freebsd.org \ / Max Laier | ICQ #67774661 X http://pf4freebsd.love2party.net/ | mla...@efnet / \ ASCII Ribbon Campaign | Against HTML Mail and News _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"