[3.18] hotplugcpu: Avoid deadlocks by waking active_writer (and dependencies)

Please consider the following for the 3.18 LTS tree to resolve deadlock problems during CPU hotplug (observed when testing mobile phone kernels).


commit 62db99f4783ea34531fc344bd8c539d5d186f24d
Author: Paul E. McKenney [off-list ref]
Date:   Wed Oct 22 14:51:49 2014 -0700

    cpu: Avoid puts_pending overflow


commit 87af9e7ff9d909e70a006ca0974466e2a1d8db0a
Author: David Hildenbrand [off-list ref]
Date:   Fri Dec 12 10:11:44 2014 +0100

    hotplugcpu: Avoid deadlocks by waking active_writer


Note that the bug addressed by 62db99f4783e is (according to the patch description) hard to tickle but taking this patch allows that later patch to cherry-pick cleanly.


Daniel.