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Subject[PATCH 09/16] ntp: Add ntp_lock to replace xtime_locking
Date
Use a ntp_lock seqlock to replace xtime_lock locking in ntp.c

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
kernel/time/ntp.c | 63 +++++++++++++++++++++++++++++++++++++----------------
1 files changed, 44 insertions(+), 19 deletions(-)
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index f131ba6..a0756b3 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -22,6 +22,9 @@
* NTP timekeeping variables:
*/

+DEFINE_SEQLOCK(ntp_lock);
+
+
/* USER_HZ period (usecs): */
unsigned long tick_usec = TICK_USEC;

@@ -133,7 +136,7 @@ static inline void pps_reset_freq_interval(void)
/**
* pps_clear - Clears the PPS state variables
*
- * Must be called while holding a write on the xtime_lock
+ * Must be called while holding a write on the ntp_lock
*/
static inline void pps_clear(void)
{
@@ -149,7 +152,7 @@ static inline void pps_clear(void)
* the last PPS signal. When it reaches 0, indicate that PPS signal is
* missing.
*
- * Must be called while holding a write on the xtime_lock
+ * Must be called while holding a write on the ntp_lock
*/
static inline void pps_dec_valid(void)
{
@@ -341,11 +344,13 @@ static void ntp_update_offset(long offset)

/**
* ntp_clear - Clears the NTP state variables
- *
- * Must be called while holding a write on the xtime_lock
*/
void ntp_clear(void)
{
+ unsigned long flags;
+
+ write_seqlock_irqsave(&ntp_lock, flags);
+
time_adjust = 0; /* stop active adjtime() */
time_status |= STA_UNSYNC;
time_maxerror = NTP_PHASE_LIMIT;
@@ -358,12 +363,21 @@ void ntp_clear(void)

/* Clear PPS state variables */
pps_clear();
+ write_sequnlock_irqrestore(&ntp_lock, flags);
+
}


u64 ntp_tick_length(void)
{
- return tick_length;
+ unsigned long seq;
+ s64 ret;
+
+ do {
+ seq = read_seqbegin(&ntp_lock);
+ ret = tick_length;
+ } while (read_seqretry(&ntp_lock, seq));
+ return ret;
}


@@ -375,14 +389,14 @@ u64 ntp_tick_length(void)
static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
{
enum hrtimer_restart res = HRTIMER_NORESTART;
+ int leap = 0;

- write_seqlock(&xtime_lock);
-
+ write_seqlock(&ntp_lock);
switch (time_state) {
case TIME_OK:
break;
case TIME_INS:
- timekeeping_leap_insert(-1);
+ leap = -1;
time_state = TIME_OOP;
printk(KERN_NOTICE
"Clock: inserting leap second 23:59:60 UTC\n");
@@ -390,7 +404,7 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
res = HRTIMER_RESTART;
break;
case TIME_DEL:
- timekeeping_leap_insert(1);
+ leap = 1;
time_tai--;
time_state = TIME_WAIT;
printk(KERN_NOTICE
@@ -405,8 +419,14 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
time_state = TIME_OK;
break;
}
+ write_sequnlock(&ntp_lock);

- write_sequnlock(&xtime_lock);
+ /*
+ * We have to call this outside of the ntp_lock to keep
+ * the proper locking hierarchy
+ */
+ if (leap)
+ timekeeping_leap_insert(leap);

return res;
}
@@ -422,6 +442,9 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
void second_overflow(void)
{
s64 delta;
+ unsigned long flags;
+
+ write_seqlock_irqsave(&ntp_lock, flags);

/* Bump the maxerror field */
time_maxerror += MAXFREQ / NSEC_PER_USEC;
@@ -441,23 +464,25 @@ void second_overflow(void)
pps_dec_valid();

if (!time_adjust)
- return;
+ goto out;

if (time_adjust > MAX_TICKADJ) {
time_adjust -= MAX_TICKADJ;
tick_length += MAX_TICKADJ_SCALED;
- return;
+ goto out;
}

if (time_adjust < -MAX_TICKADJ) {
time_adjust += MAX_TICKADJ;
tick_length -= MAX_TICKADJ_SCALED;
- return;
+ goto out;
}

tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
<< NTP_SCALE_SHIFT;
time_adjust = 0;
+out:
+ write_sequnlock_irqrestore(&ntp_lock, flags);
}

#ifdef CONFIG_GENERIC_CMOS_UPDATE
@@ -681,7 +706,7 @@ int do_adjtimex(struct timex *txc)

getnstimeofday(&ts);

- write_seqlock_irq(&xtime_lock);
+ write_seqlock_irq(&ntp_lock);

if (txc->modes & ADJ_ADJTIME) {
long save_adjust = time_adjust;
@@ -723,7 +748,7 @@ int do_adjtimex(struct timex *txc)
/* fill PPS status fields */
pps_fill_timex(txc);

- write_sequnlock_irq(&xtime_lock);
+ write_sequnlock_irq(&ntp_lock);

txc->time.tv_sec = ts.tv_sec;
txc->time.tv_usec = ts.tv_nsec;
@@ -921,7 +946,7 @@ void hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)

pts_norm = pps_normalize_ts(*phase_ts);

- write_seqlock_irqsave(&xtime_lock, flags);
+ write_seqlock_irqsave(&ntp_lock, flags);

/* clear the error bits, they will be set again if needed */
time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
@@ -934,7 +959,7 @@ void hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
* just start the frequency interval */
if (unlikely(pps_fbase.tv_sec == 0)) {
pps_fbase = *raw_ts;
- write_sequnlock_irqrestore(&xtime_lock, flags);
+ write_sequnlock_irqrestore(&ntp_lock, flags);
return;
}

@@ -949,7 +974,7 @@ void hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
time_status |= STA_PPSJITTER;
/* restart the frequency calibration interval */
pps_fbase = *raw_ts;
- write_sequnlock_irqrestore(&xtime_lock, flags);
+ write_sequnlock_irqrestore(&ntp_lock, flags);
pr_err("hardpps: PPSJITTER: bad pulse\n");
return;
}
@@ -966,7 +991,7 @@ void hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)

hardpps_update_phase(pts_norm.nsec);

- write_sequnlock_irqrestore(&xtime_lock, flags);
+ write_sequnlock_irqrestore(&ntp_lock, flags);
}
EXPORT_SYMBOL(hardpps);

--
1.7.3.2.146.gca209


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