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Neal Cardwell 2ca8877b56 nohz: Fix stale jiffies update in tick_nohz_restart() 
commit 6f103929f8 upstream.

Fix tick_nohz_restart() to not use a stale ktime_t "now" value when
calling tick_do_update_jiffies64(now).

If we reach this point in the loop it means that we crossed a tick
boundary since we grabbed the "now" timestamp, so at this point "now"
refers to a time in the old jiffy, so using the old value for "now" is
incorrect, and is likely to give us a stale jiffies value.

In particular, the first time through the loop the
tick_do_update_jiffies64(now) call is always a no-op, since the
caller, tick_nohz_restart_sched_tick(), will have already called
tick_do_update_jiffies64(now) with that "now" value.

Note that tick_nohz_stop_sched_tick() already uses the correct
approach: when we notice we cross a jiffy boundary, grab a new
timestamp with ktime_get(), and *then* update jiffies.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Link: http://lkml.kernel.org/r/1332875377-23014-1-git-send-email-ncardwell@google.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2012-04-22 16:21:25 -07:00
..
alarmtimer.c alarmtimers: Fix time comparison 2011-12-21 12:57:34 -08:00
clockevents.c Revert "clockevents: Set noop handler in clockevents_exchange_device()" 2012-01-03 10:42:00 -08:00
clocksource.c clocksource: Fix bug with max_deferment margin calculation 2011-12-09 08:52:52 -08:00
jiffies.c Fix common misspellings 2011-03-31 11:26:23 -03:00
Kconfig time: Kill off CONFIG_GENERIC_TIME 2010-07-27 12:40:54 +02:00
Makefile timers: Introduce in-kernel alarm-timer interface 2011-04-26 14:01:44 -07:00
ntp.c ntp: Fix integer overflow when setting time 2012-04-02 09:27:09 -07:00
posix-clock.c posix clocks: Replace mutex with reader/writer semaphore 2011-04-18 10:39:38 +02:00
tick-broadcast.c tick-broadcast: Stop active broadcast device when replacing it 2011-12-09 08:52:48 -08:00
tick-common.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-03-15 18:53:35 -07:00
tick-internal.h Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-03-15 18:53:35 -07:00
tick-oneshot.c time: Make do_timer() and xtime_lock local to kernel/time/ 2011-01-31 19:26:50 +01:00
tick-sched.c nohz: Fix stale jiffies update in tick_nohz_restart() 2012-04-22 16:21:25 -07:00
timecompare.c time: Use ARRAY_SIZE macro in timecompare.c 2010-10-21 17:30:06 +02:00
timeconv.c time: add function to convert between calendar time and broken-down time for universal use 2009-09-24 07:20:56 -07:00
timekeeping.c timekeeping: add arch_offset hook to ktime_get functions 2011-12-09 08:52:28 -08:00
timer_list.c timer debug: Hide kernel addresses via %pK in /proc/timer_list 2011-02-12 14:11:56 +01:00
timer_stats.c Fix common misspellings 2011-03-31 11:26:23 -03:00