Date: Thu, 30 Jul 2009 16:57:22 +0200 From: Max Laier <max@love2party.net> To: Robert Watson <rwatson@freebsd.org> Cc: freebsd-stable@freebsd.org, Matthew Fleming <matthew.fleming@isilon.com> Subject: Re: Loading ng_socket at runtime? Message-ID: <200907301657.22609.max@love2party.net> In-Reply-To: <alpine.BSF.2.00.0907301034300.29894@fledge.watson.org> References: <06D5F9F6F655AD4C92E28B662F7F853E02F6F4BC@seaxch09.desktop.isilon.com> <alpine.BSF.2.00.0907301034300.29894@fledge.watson.org>
next in thread | previous in thread | raw e-mail | index | archive | help
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, | mlaier@freebsd.org \ / Max Laier | ICQ #67774661 X http://pf4freebsd.love2party.net/ | mlaier@EFnet / \ ASCII Ribbon Campaign | Against HTML Mail and News
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200907301657.22609.max>