From c4bd822e7b12a9008241d76db45b665f2fef180c Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 21 Oct 2008 20:17:35 +0200 Subject: 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 Tested-by: Venkatesch Pallipadi --- 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 0581c11fe6c..727c1ae0517 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 -- cgit v1.2.3-70-g09d2