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  1. 12 6月, 2015 2 次提交
    • J
      time: Prevent early expiry of hrtimers[CLOCK_REALTIME] at the leap second edge · 833f32d7
      由 John Stultz 提交于 
      Currently, leapsecond adjustments are done at tick time. As a result,
the leapsecond was applied at the first timer tick *after* the
leapsecond (~1-10ms late depending on HZ), rather then exactly on the
second edge.

This was in part historical from back when we were always tick based,
but correcting this since has been avoided since it adds extra
conditional checks in the gettime fastpath, which has performance
overhead.

However, it was recently pointed out that ABS_TIME CLOCK_REALTIME
timers set for right after the leapsecond could fire a second early,
since some timers may be expired before we trigger the timekeeping
timer, which then applies the leapsecond.

This isn't quite as bad as it sounds, since behaviorally it is similar
to what is possible w/ ntpd made leapsecond adjustments done w/o using
the kernel discipline. Where due to latencies, timers may fire just
prior to the settimeofday call. (Also, one should note that all
applications using CLOCK_REALTIME timers should always be careful,
since they are prone to quirks from settimeofday() disturbances.)

However, the purpose of having the kernel do the leap adjustment is to
avoid such latencies, so I think this is worth fixing.

So in order to properly keep those timers from firing a second early,
this patch modifies the ntp and timekeeping logic so that we keep
enough state so that the update_base_offsets_now accessor, which
provides the hrtimer core the current time, can check and apply the
leapsecond adjustment on the second edge. This prevents the hrtimer
core from expiring timers too early.

This patch does not modify any other time read path, so no additional
overhead is incurred. However, this also means that the leap-second
continues to be applied at tick time for all other read-paths.

Apologies to Richard Cochran, who pushed for similar changes years
ago, which I resisted due to the concerns about the performance
overhead.

While I suspect this isn't extremely critical, folks who care about
strict leap-second correctness will likely want to watch
this. Potentially a -stable candidate eventually.
Originally-suggested-by: NRichard Cochran <richardcochran@gmail.com>
Reported-by: NDaniel Bristot de Oliveira <bristot@redhat.com>
Reported-by: NPrarit Bhargava <prarit@redhat.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1434063297-28657-4-git-send-email-john.stultz@linaro.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      833f32d7
    • J
      ntp: Introduce and use SECS_PER_DAY macro instead of 86400 · 90bf361c
      由 John Stultz 提交于 
      Currently the leapsecond logic uses what looks like magic values.

Improve this by defining SECS_PER_DAY and using that macro
to make the logic more clear.
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1434063297-28657-3-git-send-email-john.stultz@linaro.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      90bf361c
  3. 03 4月, 2015 1 次提交
  5. 01 4月, 2015 1 次提交
  7. 18 2月, 2015 1 次提交
  9. 24 1月, 2015 1 次提交
  11. 08 1月, 2015 1 次提交
  13. 24 7月, 2014 2 次提交
  15. 05 6月, 2014 1 次提交
    • J
      timekeeping: use printk_deferred when holding timekeeping seqlock · 6d9bcb62
      由 John Stultz 提交于 
      Jiri Bohac pointed out that there are rare but potential deadlock
possibilities when calling printk while holding the timekeeping
seqlock.

This is due to printk() triggering console sem wakeup, which can
cause scheduling code to trigger hrtimers which may try to read
the time.

Specifically, as Jiri pointed out, that path is:
  printk
    vprintk_emit
      console_unlock
        up(&console_sem)
          __up
	    wake_up_process
	      try_to_wake_up
	        ttwu_do_activate
		  ttwu_activate
		    activate_task
		      enqueue_task
		        enqueue_task_fair
			  hrtick_update
			    hrtick_start_fair
			      hrtick_start_fair
			        get_time
				  ktime_get
				    --> endless loop on
				    read_seqcount_retry(&timekeeper_seq, ...)

This patch tries to avoid this issue by using printk_deferred (previously
named printk_sched) which should defer printing via a irq_work_queue.
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
Reported-by: NJiri Bohac <jbohac@suse.cz>
Reviewed-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      6d9bcb62
  17. 13 5月, 2014 2 次提交
  19. 07 2月, 2014 1 次提交
  21. 12 9月, 2013 1 次提交
    • J
      timekeeping: Fix HRTICK related deadlock from ntp lock changes · 7bd36014
      由 John Stultz 提交于 
      Gerlando Falauto reported that when HRTICK is enabled, it is
possible to trigger system deadlocks. These were hard to
reproduce, as HRTICK has been broken in the past, but seemed
to be connected to the timekeeping_seq lock.

Since seqlock/seqcount's aren't supported w/ lockdep, I added
some extra spinlock based locking and triggered the following
lockdep output:

[   15.849182] ntpd/4062 is trying to acquire lock:
[   15.849765]  (&(&pool->lock)->rlock){..-...}, at: [<ffffffff810aa9b5>] __queue_work+0x145/0x480
[   15.850051]
[   15.850051] but task is already holding lock:
[   15.850051]  (timekeeper_lock){-.-.-.}, at: [<ffffffff810df6df>] do_adjtimex+0x7f/0x100

<snip>

[   15.850051] Chain exists of: &(&pool->lock)->rlock --> &p->pi_lock --> timekeeper_lock
[   15.850051]  Possible unsafe locking scenario:
[   15.850051]
[   15.850051]        CPU0                    CPU1
[   15.850051]        ----                    ----
[   15.850051]   lock(timekeeper_lock);
[   15.850051]                                lock(&p->pi_lock);
[   15.850051] lock(timekeeper_lock);
[   15.850051] lock(&(&pool->lock)->rlock);
[   15.850051]
[   15.850051]  *** DEADLOCK ***

The deadlock was introduced by 06c017fd ("timekeeping:
Hold timekeepering locks in do_adjtimex and hardpps") in 3.10

This patch avoids this deadlock, by moving the call to
schedule_delayed_work() outside of the timekeeper lock
critical section.
Reported-by: NGerlando Falauto <gerlando.falauto@keymile.com>
Tested-by: NLin Ming <minggr@gmail.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: stable <stable@vger.kernel.org> #3.11, 3.10
Link: http://lkml.kernel.org/r/1378943457-27314-1-git-send-email-john.stultz@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>
      7bd36014
  23. 23 8月, 2013 1 次提交
    • M
      ntp: Make periodic RTC update more reliable · a97ad0c4
      由 Miroslav Lichvar 提交于 
      The current code requires that the scheduled update of the RTC happens
in the closest tick to the half of the second. This seems to be
difficult to achieve reliably. The scheduled work may be missing the
target time by a tick or two and be constantly rescheduled every second.

Relax the limit to 10 ticks. As a typical RTC drifts in the 11-minute
update interval by several milliseconds, this shouldn't affect the
overall accuracy of the RTC much.
Signed-off-by: NMiroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
      a97ad0c4
  25. 29 5月, 2013 1 次提交
  27. 05 4月, 2013 6 次提交
  29. 23 3月, 2013 1 次提交
  31. 19 2月, 2013 1 次提交
  33. 09 2月, 2013 1 次提交
    • P
      time, Fix setting of hardware clock in NTP code · 84e345e4
      由 Prarit Bhargava 提交于 
      At init time, if the system time is "warped" forward in warp_clock()
it will differ from the hardware clock by sys_tz.tz_minuteswest.  This time
difference is not taken into account when ntp updates the hardware clock,
and this causes the system time to jump forward by this offset every reboot.

The kernel must take this offset into account when writing the system time
to the hardware clock in the ntp code.  This patch adds
persistent_clock_is_local which indicates that an offset has been applied
in warp_clock() and accounts for the "warp" before writing the hardware
clock.

x86 does not have this problem as rtc writes are software limited to a
+/-15 minute window relative to the current rtc time.  Other arches, such
as powerpc, however do a full synchronization of the system time to the
rtc and will see this problem.

[v2]: generated against tip/timers/core
Signed-off-by: NPrarit Bhargava <prarit@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
      84e345e4
  35. 16 1月, 2013 1 次提交
    • J
      NTP: Add a CONFIG_RTC_SYSTOHC configuration · 023f333a
      由 Jason Gunthorpe 提交于 
      The purpose of this option is to allow ARM/etc systems that rely on the
class RTC subsystem to have the same kind of automatic NTP based
synchronization that we have on PC platforms. Today ARM does not
implement update_persistent_clock and makes extensive use of the class
RTC system.

When enabled CONFIG_RTC_SYSTOHC will provide a generic
rtc_update_persistent_clock that stores the current time in the RTC and
is intended complement the existing CONFIG_RTC_HCTOSYS option that loads
the RTC at boot.

Like with RTC_HCTOSYS the platform's update_persistent_clock is used
first, if it works. Platforms with mixed class RTC and non-RTC drivers
need to return ENODEV when class RTC should be used. Such an update for
PPC is included in this patch.

Long term, implementations of update_persistent_clock should migrate to
proper class RTC drivers and use CONFIG_RTC_SYSTOHC instead.

Tested on ARM kirkwood and PPC405
Signed-off-by: NJason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
      023f333a
  37. 31 7月, 2012 1 次提交
  39. 15 7月, 2012 1 次提交
  41. 22 5月, 2012 2 次提交
  43. 24 3月, 2012 1 次提交
  45. 23 3月, 2012 1 次提交
    • J
      ntp: Fix leap-second hrtimer livelock · 6b43ae8a
      由 John Stultz 提交于 
      Since commit 7dffa3c6 the ntp
subsystem has used an hrtimer for triggering the leapsecond
adjustment. However, this can cause a potential livelock.

Thomas diagnosed this as the following pattern:
CPU 0                                                    CPU 1
do_adjtimex()
  spin_lock_irq(&ntp_lock);
    process_adjtimex_modes();				 timer_interrupt()
      process_adj_status();                                do_timer()
        ntp_start_leap_timer();                             write_lock(&xtime_lock);
          hrtimer_start();                                  update_wall_time();
             hrtimer_reprogram();                            ntp_tick_length()
               tick_program_event()                            spin_lock(&ntp_lock);
                 clockevents_program_event()
		   ktime_get()
                     seq = req_seqbegin(xtime_lock);

This patch tries to avoid the problem by reverting back to not using
an hrtimer to inject leapseconds, and instead we handle the leapsecond
processing in the second_overflow() function.

The downside to this change is that on systems that support highres
timers, the leap second processing will occur on a HZ tick boundary,
(ie: ~1-10ms, depending on HZ)  after the leap second instead of
possibly sooner (~34us in my tests w/ x86_64 lapic).

This patch applies on top of tip/timers/core.

CC: Sasha Levin <levinsasha928@gmail.com>
CC: Thomas Gleixner <tglx@linutronix.de>
Reported-by: NSasha Levin <levinsasha928@gmail.com>
Diagnoised-by: NThomas Gleixner <tglx@linutronix.de>
Tested-by: NSasha Levin <levinsasha928@gmail.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
      6b43ae8a
  47. 16 3月, 2012 1 次提交
  49. 27 1月, 2012 3 次提交
  51. 04 4月, 2011 1 次提交
  53. 19 2月, 2011 1 次提交
  55. 02 2月, 2011 1 次提交
  57. 01 2月, 2011 1 次提交