OK, I have spent quite a while bashing my head against this brick wall now, trying to suss out why the lowlatency kernel build chokes, whilst the generic does not. I suspect it is heavily buried somewhere either in the compiler flags or in the deeper headers.
This is what I have found so far: if you compile low latency, as soon as wl_cfg80211.c includes an invocation either to rtnl_lock or rtnl_unlock (a fairly essential thing to do), the compile adds a U symbol for the __rcu_read_lock and __rcu_read_unlock. Remove the all the rtnl_lock and rtnl_unlock calls and the rcu symbols vanish too. Under generic they are never there; it relies on whatever module defines rtnetlink to request those symbols. The rtnetlink.h header is identical tween the two and there is only minimal #if stuff, none of which seems to relate to low latency stuff. any ideas anyone? -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to bcmwl in Ubuntu. https://bugs.launchpad.net/bugs/1156138 Title: bcmwl-kernel-source fails to build on lowlatency kernel [FATAL: modpost: GPL-incompatible module wl.ko uses GPL-only symbol '__rcu_read_unlock'] Status in “bcmwl” package in Ubuntu: Confirmed Bug description: Ubuntu 13.04 ProblemType: Package DistroRelease: Ubuntu 13.04 Package: bcmwl-kernel-source 6.20.155.1+bdcom-0ubuntu6 ProcVersionSignature: Ubuntu 3.8.0-13.22-generic 3.8.3 Uname: Linux 3.8.0-13-generic i686 NonfreeKernelModules: wl ApportVersion: 2.9.1-0ubuntu1 Architecture: i386 DKMSKernelVersion: 3.8.0-12-lowlatency Date: Sat Mar 16 23:37:03 2013 InstallationDate: Installed on 2013-01-03 (72 days ago) InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release i386 (20121017.2) MarkForUpload: True PackageVersion: 6.20.155.1+bdcom-0ubuntu6 SourcePackage: bcmwl Title: bcmwl-kernel-source 6.20.155.1+bdcom-0ubuntu6: bcmwl kernel module failed to build UpgradeStatus: Upgraded to raring on 2013-03-12 (4 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/bcmwl/+bug/1156138/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp