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>

1 files changed, 0 insertions, 3 deletions

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index ea32405177c9..70d8a557090f 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -88,7 +88,6 @@ struct rcu_dynticks {
                                     /* Process level is worth LLONG_MAX/2. */
         int dynticks_nmi_nesting;   /* Track NMI nesting level. */
         atomic_t dynticks;          /* Even value for idle, else odd. */
-        int wake_gp_end;            /* A GP ended, need to wake up CPUs. */
 };
 
 /* RCU's kthread states for tracing. */
@@ -469,7 +468,5 @@ static void rcu_yield(void (*f)(unsigned long), unsigned long arg);
 static void rcu_cpu_kthread_setrt(int cpu, int to_rt);
 static void __cpuinit rcu_prepare_kthreads(int cpu);
 static void rcu_prepare_for_idle(int cpu);
-static void rcu_wake_cpus_for_gp_end(void);
-static void rcu_schedule_wake_gp_end(void);
 
 #endif /* #ifndef RCU_TREE_NONCORE */