linux/kernel/time
Frederic Weisbecker 24b91e360e nohz: Fix collision between tick and other hrtimers
When the tick is stopped and an interrupt occurs afterward, we check on
that interrupt exit if the next tick needs to be rescheduled. If it
doesn't need any update, we don't want to do anything.

In order to check if the tick needs an update, we compare it against the
clockevent device deadline. Now that's a problem because the clockevent
device is at a lower level than the tick itself if it is implemented
on top of hrtimer.

Every hrtimer share this clockevent device. So comparing the next tick
deadline against the clockevent device deadline is wrong because the
device may be programmed for another hrtimer whose deadline collides
with the tick. As a result we may end up not reprogramming the tick
accidentally.

In a worst case scenario under full dynticks mode, the tick stops firing
as it is supposed to every 1hz, leaving /proc/stat stalled:

      Task in a full dynticks CPU
      ----------------------------

      * hrtimer A is queued 2 seconds ahead
      * the tick is stopped, scheduled 1 second ahead
      * tick fires 1 second later
      * on tick exit, nohz schedules the tick 1 second ahead but sees
        the clockevent device is already programmed to that deadline,
        fooled by hrtimer A, the tick isn't rescheduled.
      * hrtimer A is cancelled before its deadline
      * tick never fires again until an interrupt happens...

In order to fix this, store the next tick deadline to the tick_sched
local structure and reuse that value later to check whether we need to
reprogram the clock after an interrupt.

On the other hand, ts->sleep_length still wants to know about the next
clock event and not just the tick, so we want to improve the related
comment to avoid confusion.

Reported-by: James Hartsock <hartsjc@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Rik van Riel <riel@redhat.com>
Link: http://lkml.kernel.org/r/1483539124-5693-1-git-send-email-fweisbec@gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2017-01-11 10:41:33 +01:00
..
Kconfig rcu: Drop RCU_USER_QS in favor of NO_HZ_FULL 2015-07-06 13:52:18 -07:00
Makefile posix-timers: Make them configurable 2016-11-16 09:26:35 +01:00
alarmtimer.c ktime: Cleanup ktime_set() usage 2016-12-25 17:21:22 +01:00
clockevents.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
clocksource.c clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
hrtimer.c ktime: Cleanup ktime_set() usage 2016-12-25 17:21:22 +01:00
itimer.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
jiffies.c clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
ntp.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
ntp_internal.h ntp: Fix second_overflow's input parameter type to be 64bits 2015-12-16 16:50:56 -08:00
posix-clock.c posix-clock: Fix return code on the poll method's error path 2015-12-29 11:33:06 +01:00
posix-cpu-timers.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
posix-stubs.c posix-timers: Make them configurable 2016-11-16 09:26:35 +01:00
posix-timers.c ktime: Cleanup ktime_set() usage 2016-12-25 17:21:22 +01:00
sched_clock.c timers, sched/clock: Clean up the code a bit 2015-03-27 08:34:01 +01:00
test_udelay.c time: Avoid timespec in udelay_test 2016-06-20 12:47:26 -07:00
tick-broadcast-hrtimer.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
tick-broadcast.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
tick-common.c ktime: Cleanup ktime_set() usage 2016-12-25 17:21:22 +01:00
tick-internal.h timers: Forward the wheel clock whenever possible 2016-07-07 10:35:11 +02:00
tick-oneshot.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
tick-sched.c nohz: Fix collision between tick and other hrtimers 2017-01-11 10:41:33 +01:00
tick-sched.h nohz: Fix collision between tick and other hrtimers 2017-01-11 10:41:33 +01:00
time.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
timeconst.bc timeconst: Update path in comment 2015-10-26 10:06:06 +09:00
timeconv.c time: Add time64_to_tm() 2016-06-20 12:47:15 -07:00
timecounter.c clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
timekeeping.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
timekeeping.h hrtimer: Make offset update smarter 2015-04-22 17:06:49 +02:00
timekeeping_debug.c timekeeping: Prints the amounts of time spent during suspend 2016-08-31 14:43:34 -07:00
timekeeping_internal.h clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
timer.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
timer_list.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
timer_stats.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00