1 files changed, 24 insertions, 8 deletions

diff --git a/kernel/time.c b/kernel/time.c
index f04791f69408..ffe19149d770 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -57,14 +57,17 @@ EXPORT_SYMBOL(sys_tz);
  */
 asmlinkage long sys_time(time_t __user * tloc)
 {
-        time_t i;
-        struct timeval tv;
+        /*
+         * We read xtime.tv_sec atomically - it's updated
+         * atomically by update_wall_time(), so no need to
+         * even read-lock the xtime seqlock:
+         */
+        time_t i = xtime.tv_sec;
 
-        do_gettimeofday(&tv);
-        i = tv.tv_sec;
+        smp_rmb(); /* sys_time() results are coherent */
 
         if (tloc) {
-                if (put_user(i,tloc))
+                if (put_user(i, tloc))
                         i = -EFAULT;
         }
         return i;
@@ -373,12 +376,25 @@ void do_gettimeofday (struct timeval *tv)
 
         tv->tv_sec = sec;
         tv->tv_usec = usec;
-}
 
+        /*
+         * Make sure xtime.tv_sec [returned by sys_time()] always
+         * follows the gettimeofday() result precisely. This
+         * condition is extremely unlikely, it can hit at most
+         * once per second:
+         */
+        if (unlikely(xtime.tv_sec != tv->tv_sec)) {
+                unsigned long flags;
+
+                write_seqlock_irqsave(&xtime_lock, flags);
+                update_wall_time();
+                write_sequnlock_irqrestore(&xtime_lock, flags);
+        }
+}
 EXPORT_SYMBOL(do_gettimeofday);
 
+#else   /* CONFIG_TIME_INTERPOLATION */
 
-#else
 #ifndef CONFIG_GENERIC_TIME
 /*
  * Simulate gettimeofday using do_gettimeofday which only allows a timeval
@@ -394,7 +410,7 @@ void getnstimeofday(struct timespec *tv)
 }
 EXPORT_SYMBOL_GPL(getnstimeofday);
 #endif
-#endif
+#endif  /* CONFIG_TIME_INTERPOLATION */
 
 /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
  * Assumes input in normal date format, i.e. 1980-12-31 23:59:59