The udev PKBUILD creates the /lib/udev/devices/ directory, which contains /lib/udev/devices/stdin, a symlink to /proc/self/fd/0. Grepping from /proc/self/fd/0 will hang indefinitely.

tpowa discovered this when trying to upgrade udev:
17084 ? S+ 0:00 \_ /bin/bash -e /usr/bin/makepkg -c
20886 ? S+ 0:00 \_ /bin/sh /usr/bin/fakeroot -- /usr/bin/makepkg -F -c
20901 ? S+ 0:00 \_ /bin/bash -e /usr/bin/makepkg -F -c
21604 ? S+ 0:00 \_ grep -R /home/tobias/Arch/svn/svn-packages/udev/trunk/src /home/tobias/Arch/svn/svn-packages/udev/trunk/pkg/udev

The 'grep' process blocks the packaging process. This grep is part of the new '$startdir check' introduced in 3.4.0. It now seems to be impossible to build udev without modifying makepkg (i.e., omitting that check - or is there an option?).

A possible solution might be based on find $pkgdir -type f -exec grep ..., to make sure only ordinary files are checked.