[PATCH 26/33] rcu: Don't keep the tick for RCU while in userspace

[Frederic Weisbecker]

If we are interrupting userspace, we don't need to keep
the tick for RCU: quiescent states don't need to be reported
because we soon run in userspace and local callbacks are handled
by the nocb threads.

CHECKME: Do the nocb threads actually handle the global
grace period completion for local callbacks?

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Alessio Igor Bogani <abogani@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Geoff Levand <geoff@xxxxxxxxxxxxx>
Cc: Gilad Ben Yossef <gilad@xxxxxxxxxxxxx>
Cc: Hakan Akkan <hakanakkan@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung.kim@xxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 kernel/time/tick-sched.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 1cd93a9..ecba8b7 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -22,6 +22,7 @@
 #include <linux/module.h>
 #include <linux/irq_work.h>
 #include <linux/posix-timers.h>
+#include <linux/context_tracking.h>
 
 #include <asm/irq_regs.h>
 
@@ -604,10 +605,9 @@ static bool can_stop_full_tick(int cpu)
 
 	/*
 	 * Keep the tick if we are asked to report a quiescent state.
-	 * This must be further optimized (avoid checks for local callbacks,
-	 * ignore RCU in userspace, etc...
+	 * This must be further optimized (avoid checks for local callbacks)
 	 */
-	if (rcu_pending(cpu)) {
+	if (!context_tracking_in_user() && rcu_pending(cpu)) {
 		trace_printk("Can't stop: RCU pending\n");
 		return false;
 	}
-- 
1.7.5.4

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