tree 433a07d16ff11d9f67e7991831cebf3cadfd9939
parent 84ad00cb61f1cb21f0b63bc6f7dc254399eb3830
author Paul E. McKenney <paul.mckenney@linaro.org> 1322023382 -0800
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1323628322 -0800

rcu: Eliminate RCU_FAST_NO_HZ grace-period hang

With the new implementation of RCU_FAST_NO_HZ, it was possible to hang
RCU grace periods as follows:

o	CPU 0 attempts to go idle, cycles several times through the
	rcu_prepare_for_idle() loop, then goes dyntick-idle when
	RCU needs nothing more from it, while still having at least
	on RCU callback pending.

o	CPU 1 goes idle with no callbacks.

Both CPUs can then stay in dyntick-idle mode indefinitely, preventing
the RCU grace period from ever completing, possibly hanging the system.

This commit therefore prevents CPUs that have RCU callbacks from entering
dyntick-idle mode.  This approach also eliminates the need for the
end-of-grace-period IPIs used previously.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>