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John Stultz 58bfea9532 timekeeping: Fix __ktime_get_fast_ns() regression 
In commit 27727df240 ("Avoid taking lock in NMI path with
CONFIG_DEBUG_TIMEKEEPING"), I changed the logic to open-code
the timekeeping_get_ns() function, but I forgot to include
the unit conversion from cycles to nanoseconds, breaking the
function's output, which impacts users like perf.

This results in bogus perf timestamps like:
 swapper     0 [000]   253.427536:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.426573:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.426687:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.426800:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.426905:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.427022:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.427127:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.427239:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.427346:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   254.427463:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]   255.426572:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])

Instead of more reasonable expected timestamps like:
 swapper     0 [000]    39.953768:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.064839:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.175956:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.287103:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.398217:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.509324:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.620437:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.731546:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.842654:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    40.953772:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])
 swapper     0 [000]    41.064881:  111111111 cpu-clock:  ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms])

Add the proper use of timekeeping_delta_to_ns() to convert
the cycle delta to nanoseconds as needed.

Thanks to Brendan and Alexei for finding this quickly after
the v4.8 release. Unfortunately the problematic commit has
landed in some -stable trees so they'll need this fix as
well.

Many apologies for this mistake. I'll be looking to add a
perf-clock sanity test to the kselftest timers tests soon.

Fixes: 27727df240 "timekeeping: Avoid taking lock in NMI path with CONFIG_DEBUG_TIMEKEEPING"
Reported-by: Brendan Gregg <bgregg@netflix.com>
Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Tested-and-reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable <stable@vger.kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1475636148-26539-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
 		2016-10-05 15:44:46 +02:00
..
Kconfig rcu: Drop RCU_USER_QS in favor of NO_HZ_FULL 2015-07-06 13:52:18 -07:00
Makefile time: Remove development rules from Kbuild/Makefile 2015-07-01 09:57:35 +02:00
alarmtimer.c alarmtimer: Fix comments describing structure fields 2016-06-20 12:47:09 -07:00
clockevents.c clockevents: Make clockevents_subsys static 2016-07-19 10:48:06 +02:00
clocksource.c clocksource: Defer override invalidation unless clock is unstable 2016-08-31 14:43:33 -07:00
hrtimer.c time: Avoid undefined behaviour in ktime_add_safe() 2016-08-31 14:43:36 -07:00
itimer.c itimers: Handle relative timers with CONFIG_TIME_LOW_RES proper 2016-01-17 11:13:55 +01:00
jiffies.c jiffies: Use CLOCKSOURCE_MASK instead of constant 2016-02-27 08:55:31 +01:00
ntp.c ntp: Fix ADJ_SETOFFSET being used w/ ADJ_NANO 2016-01-22 12:01:42 +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 posix_cpu_timer: Exit early when process has been reaped 2016-07-11 17:20:12 +02:00
posix-timers.c posix-timers: Handle relative timers with CONFIG_TIME_LOW_RES proper 2016-01-17 11:13:55 +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 tick/broadcast-hrtimer: Set name of the ce_broadcast_hrtimer 2016-07-05 17:02:19 +02:00
tick-broadcast.c tick: Move the export of tick_broadcast_oneshot_control to the proper place 2015-07-14 12:01:04 +02:00
tick-common.c clockevents: Remove unused set_mode() callback 2015-09-14 11:00:55 +02:00
tick-internal.h timers: Forward the wheel clock whenever possible 2016-07-07 10:35:11 +02:00
tick-oneshot.c clockevents: Provide functions to set and get the state 2015-06-02 14:40:47 +02:00
tick-sched.c tick/nohz: Prevent stopping the tick on an offline CPU 2016-09-13 17:53:52 +02:00
tick-sched.h timers/nohz: Convert tick dependency mask to atomic_t 2016-03-29 11:52:11 +02:00
time.c time: Avoid undefined behaviour in timespec64_add_safe() 2016-08-31 14:43:35 -07:00
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 timecounter: keep track of accumulated fractional nanoseconds 2014-12-30 18:29:27 -05:00
timekeeping.c timekeeping: Fix __ktime_get_fast_ns() regression 2016-10-05 15:44:46 +02:00
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: Make clocksource validation work for all clocksources 2015-12-19 15:59:57 +01:00
timer.c timers: Fix get_next_timer_interrupt() computation 2016-08-09 09:31:55 +02:00
timer_list.c hrtimer: Handle remaining time proper for TIME_LOW_RES 2016-01-17 11:13:55 +01:00
timer_stats.c timer: Avoid using timespec 2016-06-20 12:47:33 -07:00