From eudev-1.9-r2 ebuild (same applies to udev etc): CONFIG_CHECK="~BLK_DEV_BSG ~DEVTMPFS ~!IDE ~INOTIFY_USER ~!SYSFS_DEPRECATED ~!SYSFS_DEPRECATED_V2 ~SIGNALFD ~EPOLL ~FHANDLE ~NET" The default config does not enable FHANDLE, which can cause random weirdness. Please enable it by default.
+ 14 Aug 2014; Patrick Lauer <patrick@gentoo.org> +genkernel-3.4.51.1-r1.ebuild: + Bump with new kernel configs for x86,amd64. Adds fhandle etc. for udev and + some other useful things. Sigh.
A patch to resolve this has been committed to git. It will be included in the next tag: https://git.overlays.gentoo.org/gitweb/?p=proj/genkernel.git;a=commit;h=6bb3ac22b4f6cd0bdbed1206c4309ef289a48fcb
Fixed in 3.4.51.2.