Revert "atomic: use <linux/atomic.h>"

This reverts commit 52bac7528da4b4c351cd8fad132d8f88e386a297.
Revert "Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip"

This reverts commit 2ca548fc3eb9f18a2f8666b80b1560ea56d642ae.