cpu: Avoid puts_pending overflow

A long string of get_online_cpus() with each followed by a
put_online_cpu() that fails to acquire cpu_hotplug.lock can result in
overflow of the cpu_hotplug.puts_pending counter.  Although this is
perhaps improbably, a system with absolutely no CPU-hotplug operations
will have an arbitrarily long time in which this overflow could occur.
This commit therefore adds overflow checks to get_online_cpus() and
try_get_online_cpus().

Change-Id: Iaac6c81b4cc34946a9769f1a3b4aa39fa3eb8ef3
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
Git-commit: 62db99f4783ea34531fc344bd8c539d5d186f24d
Git-repo: https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git


Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>