[PATCH 22/32] rcu: Restart tick if we enqueue a callback in a nohz/cpuset CPU

[Frederic Weisbecker]

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: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Anton Blanchard <anton@xxxxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Cc: Paul E . McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tim Pepper <lnxninja@xxxxxxxxxxxxxxxxxx>
---
 kernel/rcutree.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d496c70..b5643ce2 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -51,6 +51,7 @@
 #include <linux/kthread.h>
 #include <linux/prefetch.h>
 #include <linux/cpuset.h>
+#include <linux/tick.h>
 
 #include "rcutree.h"
 
@@ -1546,6 +1547,13 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
 	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
 	rdp->qlen++;
 
+	/* Restart the timer if needed to handle the callbacks */
+	if (tick_nohz_adaptive_mode()) {
+		/* Make updates on nxtlist visible to self IPI */
+		barrier();
+		smp_cpuset_update_nohz(smp_processor_id());
+	}
+
 	/* If interrupts were disabled, don't dive into RCU core. */
 	if (irqs_disabled_flags(flags)) {
 		local_irq_restore(flags);
-- 
1.7.5.4

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