linux-stable.git/kernel/time/timekeeping.c, branch v4.4.4

time: Avoid signed overflow in timekeeping_get_ns()

2016-03-03T23:07:16+00:00

commit 35a4933a895927990772ae96fdcfd2f806929ee2 upstream.

1e75fa8 "time: Condense timekeeper.xtime into xtime_sec" replaced a call to
clocksource_cyc2ns() from timekeeping_get_ns() with an open-coded version
of the same logic to avoid keeping a semi-redundant struct timespec
in struct timekeeper.

However, the commit also introduced a subtle semantic change - where
clocksource_cyc2ns() uses purely unsigned math, the new version introduces
a signed temporary, meaning that if (delta * tk->mult) has a 63-bit
overflow the following shift will still give a negative result.  The
choice of 'maxsec' in __clocksource_updatefreq_scale() means this will
generally happen if there's a ~10 minute pause in examining the
clocksource.

This can be triggered on a powerpc KVM guest by stopping it from qemu for
a bit over 10 minutes.  After resuming time has jumped backwards several
minutes causing numerous problems (jiffies does not advance, msleep()s can
be extended by minutes..).  It doesn't happen on x86 KVM guests, because
the guest TSC is effectively frozen while the guest is stopped, which is
not the case for the powerpc timebase.

Obviously an unsigned (64 bit) overflow will only take twice as long as a
signed, 63-bit overflow.  I don't know the time code well enough to know
if that will still cause incorrect calculations, or if a 64-bit overflow
is avoided elsewhere.

Still, an incorrect forwards clock adjustment will cause less trouble than
time going backwards.  So, this patch removes the potential for
intermediate signed overflow.

Suggested-by: Laurent Vivier 
Tested-by: Laurent Vivier 
Signed-off-by: David Gibson 
Signed-off-by: John Stultz 
Signed-off-by: Greg Kroah-Hartman

remove abs64()

2015-11-09T23:11:24+00:00

Switch everything to the new and more capable implementation of abs().
Mainly to give the new abs() a bit of a workout.

Cc: Michal Nazarewicz 
Cc: John Stultz 
Cc: Ingo Molnar 
Cc: Steven Rostedt 
Cc: Peter Zijlstra 
Cc: Masami Hiramatsu 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2015-11-03T22:13:41+00:00

Pull timer updates from Thomas Gleixner:
 "The timer departement provides:

   - More y2038 work in the area of ntp and pps.

   - Optimization of posix cpu timers

   - New time related selftests

   - Some new clocksource drivers

   - The usual pile of fixes, cleanups and improvements"

* 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits)
  timeconst: Update path in comment
  timers/x86/hpet: Type adjustments
  clocksource/drivers/armada-370-xp: Implement ARM delay timer
  clocksource/drivers/tango_xtal: Add new timer for Tango SoCs
  clocksource/drivers/imx: Allow timer irq affinity change
  clocksource/drivers/exynos_mct: Use container_of() instead of this_cpu_ptr()
  clocksource/drivers/h8300_*: Remove unneeded memset()s
  clocksource/drivers/sh_cmt: Remove unneeded memset() in sh_cmt_setup()
  clocksource/drivers/em_sti: Remove unneeded memset()s
  clocksource/drivers/mediatek: Use GPT as sched clock source
  clockevents/drivers/mtk: Fix spurious interrupt leading to crash
  posix_cpu_timer: Reduce unnecessary sighand lock contention
  posix_cpu_timer: Convert cputimer->running to bool
  posix_cpu_timer: Check thread timers only when there are active thread timers
  posix_cpu_timer: Optimize fastpath_timer_check()
  timers, kselftest: Add 'adjtick' test to validate adjtimex() tick adjustments
  timers: Use __fls in apply_slack()
  clocksource: Remove return statement from void functions
  net: sfc: avoid using timespec
  ntp/pps: use y2038 safe types in pps_event_time
  ...

Merge branch 'fortglx/4.4/time' of https://git.linaro.org/people/john.stultz/linux into timers/core

2015-10-20T10:36:37+00:00

Time updates from John Stultz:

     - More 2038 work from Arnd Bergmann around ntp and pps

timekeeping: Increment clock_was_set_seq in timekeeping_init()

2015-10-16T13:50:22+00:00

timekeeping_init() can set the wall time offset, so we need to
increment the clock_was_set_seq counter. That way hrtimers will pick
up the early offset immediately. Otherwise on a machine which does not
set wall time later in the boot process the hrtimer offset is stale at
0 and wall time timers are going to expire with a delay of 45 years.

Fixes: 868a3e915f7f "hrtimer: Make offset update smarter"
Reported-and-tested-by: Heiko Carstens 
Signed-off-by: Thomas Gleixner 
Cc: Stefan Liebler 
Cc: Peter Zijlstra 
Cc: John Stultz

ntp/pps: replace getnstime_raw_and_real with 64-bit version

2015-10-01T16:59:01+00:00

There is exactly one caller of getnstime_raw_and_real in the kernel,
which is the pps_get_ts function. This changes the caller and
the implementation to work on timespec64 types rather than timespec,
to avoid the time_t overflow on 32-bit architectures.

For consistency with the other new functions (ktime_get_seconds,
ktime_get_real_*, ...), I'm renaming the function to
ktime_get_raw_and_real_ts64.

We still need to convert from the internal 64-bit type to 32 bit
types in the caller, but this conversion is now pushed out from
getnstime_raw_and_real to pps_get_ts. A follow-up patch changes
the remaining pps code to completely avoid the conversion.

Acked-by: Richard Cochran 
Acked-by: David S. Miller 
Reviewed-by: Thomas Gleixner 
Signed-off-by: Arnd Bergmann 
Signed-off-by: John Stultz

ntp/pps: use timespec64 for hardpps()

2015-10-01T16:57:59+00:00

There is only one user of the hardpps function in the kernel, so
it makes sense to atomically change it over to using 64-bit
timestamps for y2038 safety. In the hardpps implementation,
we also need to change the pps_normtime structure, which is
similar to struct timespec and also requires a 64-bit
seconds portion.

This introduces two temporary variables in pps_kc_event() to
do the conversion, they will be removed again in the next step,
which seemed preferable to having a larger patch changing it
all at the same time.

Acked-by: Richard Cochran 
Acked-by: David S. Miller 
Reviewed-by: Thomas Gleixner 
Signed-off-by: Arnd Bergmann 
Signed-off-by: John Stultz

time: Fix spelling in comments

2015-09-22T10:54:23+00:00

Signed-off-by: Zhen Lei 
Cc: Hanjun Guo 
Cc: John Stultz 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Rafael J. Wysocki 
Cc: Thomas Gleixner 
Cc: Tianhong Ding 
Cc: Viresh Kumar 
Cc: Xinwei Hu 
Cc: Xunlei Pang 
Cc: Zefan Li 
Link: http://lkml.kernel.org/r/1440484973-13892-1-git-send-email-thunder.leizhen@huawei.com
[ Fixed yet another typo in one of the sentences fixed. ]
Signed-off-by: Ingo Molnar

time: Fix timekeeping_freqadjust()'s incorrect use of abs() instead of abs64()

2015-09-13T08:30:47+00:00

The internal clocksteering done for fine-grained error
correction uses a logarithmic approximation, so any time
adjtimex() adjusts the clock steering, timekeeping_freqadjust()
quickly approximates the correct clock frequency over a series
of ticks.

Unfortunately, the logic in timekeeping_freqadjust(), introduced
in commit:

  dc491596f639 ("timekeeping: Rework frequency adjustments to work better w/ nohz")

used the abs() function with a s64 error value to calculate the
size of the approximated adjustment to be made.

Per include/linux/kernel.h:

  "abs() should not be used for 64-bit types (s64, u64, long long) - use abs64()".

Thus on 32-bit platforms, this resulted in the clocksteering to
take a quite dampended random walk trying to converge on the
proper frequency, which caused the adjustments to be made much
slower then intended (most easily observed when large
adjustments are made).

This patch fixes the issue by using abs64() instead.

Reported-by: Nuno Gonçalves 
Tested-by: Nuno Goncalves 
Signed-off-by: John Stultz 
Cc:  # v3.17+
Cc: Linus Torvalds 
Cc: Miroslav Lichvar 
Cc: Peter Zijlstra 
Cc: Prarit Bhargava 
Cc: Richard Cochran 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1441840051-20244-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar

time: Introduce current_kernel_time64()

2015-08-17T18:25:35+00:00

The current_kernel_time() is not year 2038 safe on 32bit systems
since it returns a timespec value. Introduce current_kernel_time64()
which returns a timespec64 value.

Cc: Prarit Bhargava 
Cc: Richard Cochran 
Cc: Ingo Molnar 
Cc: Thomas Gleixner 
Signed-off-by: Baolin Wang 
Signed-off-by: John Stultz