linux-toradex.git/kernel/time/ntp.c, branch v3.2.39

ntp: Correct TAI offset during leap second

2012-07-25T03:11:33+00:00

commit dd48d708ff3e917f6d6b6c2b696c3f18c019feed upstream.

When repeating a UTC time value during a leap second (when the UTC
time should be 23:59:60), the TAI timescale should not stop. The kernel
NTP code increments the TAI offset one second too late. This patch fixes
the issue by incrementing the offset during the leap second itself.

Signed-off-by: Richard Cochran 
Signed-off-by: John Stultz 
Signed-off-by: Ben Hutchings

ntp: Fix leap-second hrtimer livelock

2012-07-25T03:11:32+00:00

This is a backport of 6b43ae8a619d17c4935c3320d2ef9e92bdeed05d

This should have been backported when it was commited, but I
mistook the problem as requiring the ntp_lock changes
that landed in 3.4 in order for it to occur.

Unfortunately the same issue can happen (with only one cpu)
as follows:
do_adjtimex()
 write_seqlock_irq(&xtime_lock);
  process_adjtimex_modes()
   process_adj_status()
    ntp_start_leap_timer()
     hrtimer_start()
      hrtimer_reprogram()
       tick_program_event()
        clockevents_program_event()
         ktime_get()
          seq = req_seqbegin(xtime_lock); [DEADLOCK]

This deadlock will no always occur, as it requires the
leap_timer to force a hrtimer_reprogram which only happens
if its set and there's no sooner timer to expire.

NOTE: This patch, being faithful to the original commit,
introduces a bug (we don't update wall_to_monotonic),
which will be resovled by backporting a following fix.

Original commit message below:

Since commit 7dffa3c673fbcf835cd7be80bb4aec8ad3f51168 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 
CC: Thomas Gleixner 
Reported-by: Sasha Levin 
Diagnoised-by: Thomas Gleixner 
Tested-by: Sasha Levin 
Cc: Prarit Bhargava 
Cc: Thomas Gleixner 
Cc: Linux Kernel 
Signed-off-by: John Stultz 
Signed-off-by: Ben Hutchings

ntp: Fix integer overflow when setting time

2012-04-02T16:52:35+00:00

commit a078c6d0e6288fad6d83fb6d5edd91ddb7b6ab33 upstream.

'long secs' is passed as divisor to div_s64, which accepts a 32bit
divisor. On 64bit machines that value is trimmed back from 8 bytes
back to 4, causing a divide by zero when the number is bigger than
(1 << 32) - 1 and all 32 lower bits are 0.

Use div64_long() instead.

Signed-off-by: Sasha Levin 
Cc: johnstul@us.ibm.com
Link: http://lkml.kernel.org/r/1331829374-31543-2-git-send-email-levinsasha928@gmail.com
Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

ntp: fix non privileged system time shifting

2011-04-04T15:31:23+00:00

The ADJ_SETOFFSET bit added in commit 094aa188 ("ntp: Add ADJ_SETOFFSET
mode bit") also introduced a way for any user to change the system time.
Sneaky or buggy calls to adjtimex() could set

    ADJ_OFFSET_SS_READ | ADJ_SETOFFSET

which would result in a successful call to timekeeping_inject_offset().
This patch fixes the issue by adding the capability check.

Signed-off-by: Richard Cochran 
Signed-off-by: Linus Torvalds

ntp: Remove redundant and incorrect parameter check

2011-02-18T16:01:12+00:00

The ADJ_SETOFFSET code redundantly checks the range of the nanoseconds
field of the time value. This field is checked again in the subsequent
call to timekeeping_inject_offset(). Also, as is, the check will not
detect whether the number of microseconds is out of range.

Let timekeeping_inject_offset() do the error checking.
 
Signed-off-by: Richard Cochran 
Cc: johnstul@us.ibm.com
LKML-Reference: <20110218090724.GA2924@riccoc20.at.omicron.at>
Signed-off-by: Thomas Gleixner

ntp: Add ADJ_SETOFFSET mode bit

2011-02-02T14:28:18+00:00

This patch adds a new mode bit into the timex structure. When set, the bit
instructs the kernel to add the given time value to the current time.

Signed-off-by: Richard Cochran 
Acked-by: John Stultz 
LKML-Reference: <20110201134320.688829863@linutronix.de>
Signed-off-by: Thomas Gleixner

time: Make do_timer() and xtime_lock local to kernel/time/

2011-01-31T18:26:50+00:00

All callers of do_timer() are converted to xtime_update(). The only
users of xtime_lock are in kernel/time/. Make both local to
kernel/time/ and remove them from the global header files.

[ tglx: Reuse tick-internal.h instead of creating another local header
  	file. Massaged changelog ]

Signed-off-by: Torben Hohn 
Cc: Peter Zijlstra 
Cc: johnstul@us.ibm.com
Cc: yong.zhang0@gmail.com
Cc: hch@infradead.org
Signed-off-by: Thomas Gleixner

ntp: add hardpps implementation

2011-01-13T16:03:20+00:00

This commit adds hardpps() implementation based upon the original one from
the NTPv4 reference kernel code from David Mills.  However, it is highly
optimized towards very fast syncronization and maximum stickness to PPS
signal.  The typical error is less then a microsecond.

To make it sync faster I had to throw away exponential phase filter so
that the full phase offset is corrected immediately.  Then I also had to
throw away median phase filter because it gives a bigger error itself if
used without exponential filter.

Maybe we will find an appropriate filtering scheme in the future but it's
not necessary if the signal quality is ok.

Signed-off-by: Alexander Gordeev 
Acked-by: John Stultz 
Cc: Rodolfo Giometti 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ntp: Clamp PLL update interval

2010-09-09T18:48:37+00:00

Clamp update interval to reduce PLL gain with low sampling rate (e.g.
intermittent network connection) to avoid instability.

The clamp roughly corresponds to the loop time constant, it's 8 * poll
interval for SHIFT_PLL 2 and 32 * poll interval for SHIFT_PLL 4. This
gives good results without affecting the gain in normal conditions where
ntpd skips only up to seven consecutive samples.

Signed-off-by: Miroslav Lichvar 
Acked-by: john stultz 
LKML-Reference: <1283870626-9472-1-git-send-email-mlichvar@redhat.com>
Signed-off-by: Thomas Gleixner

ntp: Make time_adjust static

2010-03-23T16:19:37+00:00

Now that no arches are accessing time_adjust directly,
make it static.

Signed-off-by: John Stultz 
LKML-Reference: <1268968769-19209-1-git-send-email-johnstul@us.ibm.com>
Signed-off-by: Thomas Gleixner