From: Nathan Lynch <nathanl@austin.ibm.com>

On some systems it can take a hotplugged cpu much longer to come up than it
would at boot.  If the cpu comes up after we've given up on it, it tends to
die in its first attempt to kmem_cache_alloc (uninitialized percpu data, I
imagine).

In my experimentation I haven't seen a processor take more than one second
to become available; the patch waits five seconds just to be safe.
Signed-off-by: Nathan Lynch <nathanl@austin.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>