[PATCH 3.11 158/198] nohz: Fix another inconsistency between CONFIG_NO_HZ=n and nohz=off

[Luis Henriques]

3.11.10.13 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx at linutronix.de>

commit 0e576acbc1d9600cf2d9b4a141a2554639959d50 upstream.

If CONFIG_NO_HZ=n tick_nohz_get_sleep_length() returns NSEC_PER_SEC/HZ.

If CONFIG_NO_HZ=y and the nohz functionality is disabled via the
command line option "nohz=off" or not enabled due to missing hardware
support, then tick_nohz_get_sleep_length() returns 0. That happens
because ts->sleep_length is never set in that case.

Set it to NSEC_PER_SEC/HZ when the NOHZ mode is inactive.

Reported-by: Michal Hocko <mhocko at suse.cz>
Reported-by: Borislav Petkov <bp at alien8.de>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: Rui Xiang <rui.xiang at huawei.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/time/tick-sched.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index e8a1516cc0a3..9e62bdc9b095 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -714,8 +714,10 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 		return false;
 	}
 
-	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
+	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
+		ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
 		return false;
+	}
 
 	if (need_resched())
 		return false;
-- 
1.9.1