[PATCH] ntp: avoid time_offset overflows

I've been seeing some odd NTP behavior recently on a few boxes and
finally narrowed it down to time_offset overflowing when converted to
SHIFT_UPDATE units (which was a side effect from my HZfreeNTP patch).

This patch converts time_offset from a long to a s64 which resolves the
issue.

[tglx@linutronix.de: signedness fixes]
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 14 deletions

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index eb12509e00bd..cb25649c6f50 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -32,7 +32,7 @@ static u64 tick_length, tick_length_base;
 /* TIME_ERROR prevents overwriting the CMOS clock */
 static int time_state = TIME_OK;        /* clock synchronization status */
 int time_status = STA_UNSYNC;           /* clock status bits            */
-static long time_offset;                /* time adjustment (ns)         */
+static s64 time_offset;         /* time adjustment (ns)         */
 static long time_constant = 2;          /* pll time constant            */
 long time_maxerror = NTP_PHASE_LIMIT;   /* maximum error (us)           */
 long time_esterror = NTP_PHASE_LIMIT;   /* estimated error (us)         */
@@ -196,7 +196,7 @@ void __attribute__ ((weak)) notify_arch_cmos_timer(void)
  */
 int do_adjtimex(struct timex *txc)
 {
-        long ltemp, mtemp, save_adjust;
+        long mtemp, save_adjust, rem;
         s64 freq_adj, temp64;
         int result;
 
@@ -277,14 +277,14 @@ int do_adjtimex(struct timex *txc)
                     time_adjust = txc->offset;
                 }
                 else if (time_status & STA_PLL) {
-                    ltemp = txc->offset * NSEC_PER_USEC;
+                    time_offset = txc->offset * NSEC_PER_USEC;
 
                     /*
                      * Scale the phase adjustment and
                      * clamp to the operating range.
                      */
-                    time_offset = min(ltemp, MAXPHASE * NSEC_PER_USEC);
-                    time_offset = max(time_offset, -MAXPHASE * NSEC_PER_USEC);
+                    time_offset = min(time_offset, (s64)MAXPHASE * NSEC_PER_USEC);
+                    time_offset = max(time_offset, (s64)-MAXPHASE * NSEC_PER_USEC);
 
                     /*
                      * Select whether the frequency is to be controlled
@@ -297,11 +297,11 @@ int do_adjtimex(struct timex *txc)
                     mtemp = xtime.tv_sec - time_reftime;
                     time_reftime = xtime.tv_sec;
 
-                    freq_adj = (s64)time_offset * mtemp;
+                    freq_adj = time_offset * mtemp;
                     freq_adj = shift_right(freq_adj, time_constant * 2 +
                                            (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
                     if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
-                        temp64 = (s64)time_offset << (SHIFT_NSEC - SHIFT_FLL);
+                        temp64 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
                         if (time_offset < 0) {
                             temp64 = -temp64;
                             do_div(temp64, mtemp);
@@ -314,8 +314,10 @@ int do_adjtimex(struct timex *txc)
                     freq_adj += time_freq;
                     freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
                     time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
-                    time_offset = (time_offset / NTP_INTERVAL_FREQ)
-                                        << SHIFT_UPDATE;
+                    time_offset = div_long_long_rem_signed(time_offset,
+                                                           NTP_INTERVAL_FREQ,
+                                                           &rem);
+                    time_offset <<= SHIFT_UPDATE;
                 } /* STA_PLL */
             } /* txc->modes & ADJ_OFFSET */
             if (txc->modes & ADJ_TICK)
@@ -328,12 +330,12 @@ leave:	if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
                 result = TIME_ERROR;
 
         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
-            txc->offset    = save_adjust;
+                txc->offset = save_adjust;
         else
-            txc->offset    = shift_right(time_offset, SHIFT_UPDATE)
-                                * NTP_INTERVAL_FREQ / 1000;
-        txc->freq          = (time_freq / NSEC_PER_USEC)
-                                << (SHIFT_USEC - SHIFT_NSEC);
+                txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *
+                                NTP_INTERVAL_FREQ / 1000;
+        txc->freq          = (time_freq / NSEC_PER_USEC) <<
+                                (SHIFT_USEC - SHIFT_NSEC);
         txc->maxerror      = time_maxerror;
         txc->esterror      = time_esterror;
         txc->status        = time_status;