[PATCH 20/32] nohz/cpuset: Restart the tick if printk needs it

[Frederic Weisbecker]

If we are in nohz adaptive mode and printk is called, the tick is
missing to wake up the logger. We need to restart the tick when that
happens.

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/printk.c |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index 3518539..aff07f0 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -41,6 +41,7 @@
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 #include <linux/rculist.h>
+#include <linux/tick.h>
 
 #include <asm/uaccess.h>
 
@@ -1220,8 +1221,22 @@ int printk_needs_cpu(int cpu)
 
 void wake_up_klogd(void)
 {
-	if (waitqueue_active(&log_wait))
+	unsigned long flags;
+
+	if (waitqueue_active(&log_wait)) {
 		this_cpu_write(printk_pending, 1);
+		/* Make it visible from any interrupt from now */
+		barrier();
+		/*
+		 * It's safe to check that even if interrupts are not disabled.
+		 * If we enable nohz adaptive mode concurrently, we'll the
+		 * printk_pending value and thus keep a periodic tick behaviour.
+		 * Unless it's possible tick_nohz_adaptive_mode() reads its value
+		 * before the barrier() ?
+		 */
+		if (tick_nohz_adaptive_mode())
+			smp_cpuset_update_nohz(smp_processor_id());
+	}
 }
 
 /**
-- 
1.7.5.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/