[PATCH 12/32] rcu: Restart tick if we enqueue a callback in a nohz/cpuset CPU

[Steven Rostedt]

From: Frederic Weisbecker <fweisbec@xxxxxxxxx>

If we enqueue an rcu callback, we need the CPU tick to stay
alive until we take care of those by completing the appropriate
grace period.

Thus, when we call_rcu(), send a self IPI that checks rcu_needs_cpu()
so that we restore a periodic tick behaviour that can take care of
everything.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Alessio Igor Bogani <abogani@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Cc: Geoff Levand <geoff@xxxxxxxxxxxxx>
Cc: Gilad Ben Yossef <gilad@xxxxxxxxxxxxx>
Cc: Hakan Akkan <hakanakkan@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Kevin Hilman <khilman@xxxxxx>
Cc: Max Krasnyansky <maxk@xxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Sven-Thorsten Dietrich <thebigcorporation@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/rcutree.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 21664a3..7dce432 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2081,6 +2081,13 @@ static void invoke_rcu_core(void)
 static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
 			    struct rcu_head *head, unsigned long flags)
 {
+	/* Restart the timer if needed to handle the callbacks */
+	if (cpuset_adaptive_nohz()) {
+		/* Make updates on nxtlist visible to self IPI */
+		barrier();
+		smp_cpuset_update_nohz(smp_processor_id());
+	}
+
 	/*
 	 * If called from an extended quiescent state, invoke the RCU
 	 * core in order to force a re-evaluation of RCU's idleness.
-- 
1.7.10.4


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