From c4bd822e7b12a9008241d76db45b665f2fef180c Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 21 Oct 2008 20:17:35 +0200
Subject: [PATCH] NOHZ: fix thinko in the timer restart code path
commit fb02fbc14d17837b4b7b02dbb36142c16a7bf208 (NOHZ: restart tick
device from irq_enter())
solves the problem of stale jiffies when long running softirqs happen
in a long idle sleep period, but it has a major thinko in it:
When the interrupt which came in _is_ the timer interrupt which should
expire ts->sched_timer then we cancel and rearm the timer _before_ it
gets expired in hrtimer_interrupt() to the next period. That means the
call back function is not called. This game can go on for ever :(
Prevent this by making sure to only rearm the timer when the expiry
time is more than one tick_period away. Otherwise keep it running as
it is either already expired or will expiry at the right point to
update jiffies.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Venkatesch Pallipadi <venkatesh.pallipadi@intel.com>
---
kernel/time/tick-sched.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 0581c11fe6c6..727c1ae0517a 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -567,11 +567,21 @@ static void tick_nohz_switch_to_nohz(void)
static void tick_nohz_kick_tick(int cpu)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ ktime_t delta, now;
if (!ts->tick_stopped)
return;
- tick_nohz_restart(ts, ktime_get());
+ /*
+ * Do not touch the tick device, when the next expiry is either
+ * already reached or less/equal than the tick period.
+ */
+ now = ktime_get();
+ delta = ktime_sub(ts->sched_timer.expires, now);
+ if (delta.tv64 <= tick_period.tv64)
+ return;
+
+ tick_nohz_restart(ts, now);
}
#else
--
2.34.1