1 files changed, 34 insertions, 14 deletions

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 2a7ddc579379..86f7e3d154d8 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -283,9 +283,9 @@ static inline void update_gtod(u64 new_tb_stamp, u64 new_stamp_xsec,
          * the two values of tb_update_count match and are even then the
          * tb_to_xs and stamp_xsec values are consistent.  If not, then it
          * loops back and reads them again until this criteria is met.
+         * We expect the caller to have done the first increment of
+         * vdso_data->tb_update_count already.
          */
-        ++(vdso_data->tb_update_count);
-        smp_wmb();
         vdso_data->tb_orig_stamp = new_tb_stamp;
         vdso_data->stamp_xsec = new_stamp_xsec;
         vdso_data->tb_to_xs = new_tb_to_xs;
@@ -310,20 +310,15 @@ static __inline__ void timer_recalc_offset(u64 cur_tb)
         unsigned long offset;
         u64 new_stamp_xsec;
         u64 tlen, t2x;
+        u64 tb, xsec_old, xsec_new;
+        struct gettimeofday_vars *varp;
 
         if (__USE_RTC())
                 return;
         tlen = current_tick_length();
         offset = cur_tb - do_gtod.varp->tb_orig_stamp;
-        if (tlen == last_tick_len && offset < 0x80000000u) {
-                /* check that we're still in sync; if not, resync */
-                struct timeval tv;
-                __do_gettimeofday(&tv, cur_tb);
-                if (tv.tv_sec <= xtime.tv_sec &&
-                    (tv.tv_sec < xtime.tv_sec ||
-                     tv.tv_usec * 1000 <= xtime.tv_nsec))
-                        return;
-        }
+        if (tlen == last_tick_len && offset < 0x80000000u)
+                return;
         if (tlen != last_tick_len) {
                 t2x = mulhdu(tlen << TICKLEN_SHIFT, ticklen_to_xs);
                 last_tick_len = tlen;
@@ -332,6 +327,21 @@ static __inline__ void timer_recalc_offset(u64 cur_tb)
         new_stamp_xsec = (u64) xtime.tv_nsec * XSEC_PER_SEC;
         do_div(new_stamp_xsec, 1000000000);
         new_stamp_xsec += (u64) xtime.tv_sec * XSEC_PER_SEC;
+
+        ++vdso_data->tb_update_count;
+        smp_mb();
+
+        /*
+         * Make sure time doesn't go backwards for userspace gettimeofday.
+         */
+        tb = get_tb();
+        varp = do_gtod.varp;
+        xsec_old = mulhdu(tb - varp->tb_orig_stamp, varp->tb_to_xs)
+                + varp->stamp_xsec;
+        xsec_new = mulhdu(tb - cur_tb, t2x) + new_stamp_xsec;
+        if (xsec_new < xsec_old)
+                new_stamp_xsec += xsec_old - xsec_new;
+
         update_gtod(cur_tb, new_stamp_xsec, t2x);
 }
 
@@ -564,6 +574,10 @@ int do_settimeofday(struct timespec *tv)
         }
 #endif
 
+        /* Make userspace gettimeofday spin until we're done. */
+        ++vdso_data->tb_update_count;
+        smp_mb();
+
         /*
          * Subtract off the number of nanoseconds since the
          * beginning of the last tick.
@@ -724,10 +738,16 @@ void __init time_init(void)
          * It is computed as:
          * ticklen_to_xs = 2^N / (tb_ticks_per_jiffy * 1e9)
          * where N = 64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT
-         * so as to give the result as a 0.64 fixed-point fraction.
+         * which turns out to be N = 51 - SHIFT_HZ.
+         * This gives the result as a 0.64 fixed-point fraction.
+         * That value is reduced by an offset amounting to 1 xsec per
+         * 2^31 timebase ticks to avoid problems with time going backwards
+         * by 1 xsec when we do timer_recalc_offset due to losing the
+         * fractional xsec.  That offset is equal to ppc_tb_freq/2^51
+         * since there are 2^20 xsec in a second.
          */
-        div128_by_32(1ULL << (64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT), 0,
-                     tb_ticks_per_jiffy, &res);
+        div128_by_32((1ULL << 51) - ppc_tb_freq, 0,
+                     tb_ticks_per_jiffy << SHIFT_HZ, &res);
         div128_by_32(res.result_high, res.result_low, NSEC_PER_SEC, &res);
         ticklen_to_xs = res.result_low;