1 files changed, 51 insertions, 3 deletions

diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index e34e1effe0f5..ef02d941c2ad 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -59,7 +59,7 @@ long long disable_timer(void)
 {
         struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } });
 
-        if(setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
+        if (setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
                 printk(UM_KERN_ERR "disable_timer - setitimer failed, "
                        "errno = %d\n", errno);
 
@@ -74,13 +74,61 @@ long long os_nsecs(void)
         return timeval_to_ns(&tv);
 }
 
+#ifdef UML_CONFIG_NO_HZ
+static int after_sleep_interval(struct timespec *ts)
+{
+}
+#else
+static inline long long timespec_to_us(const struct timespec *ts)
+{
+        return ((long long) ts->tv_sec * UM_USEC_PER_SEC) +
+                ts->tv_nsec / UM_NSEC_PER_USEC;
+}
+
+static int after_sleep_interval(struct timespec *ts)
+{
+        int usec = UM_USEC_PER_SEC / UM_HZ;
+        long long start_usecs = timespec_to_us(ts);
+        struct timeval tv;
+        struct itimerval interval;
+
+        /*
+         * It seems that rounding can increase the value returned from
+         * setitimer to larger than the one passed in.  Over time,
+         * this will cause the remaining time to be greater than the
+         * tick interval.  If this happens, then just reduce the first
+         * tick to the interval value.
+         */
+        if (start_usecs > usec)
+                start_usecs = usec;
+        tv = ((struct timeval) { .tv_sec  = start_usecs / UM_USEC_PER_SEC,
+                                 .tv_usec = start_usecs % UM_USEC_PER_SEC });
+        interval = ((struct itimerval) { { 0, usec }, tv });
+
+        if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
+                return -errno;
+
+        return 0;
+}
+#endif
+
 extern void alarm_handler(int sig, struct sigcontext *sc);
 
 void idle_sleep(unsigned long long nsecs)
 {
-        struct timespec ts = { .tv_sec  = nsecs / UM_NSEC_PER_SEC,
-                               .tv_nsec = nsecs % UM_NSEC_PER_SEC };
+        struct timespec ts;
+
+        /*
+         * nsecs can come in as zero, in which case, this starts a
+         * busy loop.  To prevent this, reset nsecs to the tick
+         * interval if it is zero.
+         */
+        if (nsecs == 0)
+                nsecs = UM_NSEC_PER_SEC / UM_HZ;
+        ts = ((struct timespec) { .tv_sec       = nsecs / UM_NSEC_PER_SEC,
+                                  .tv_nsec      = nsecs % UM_NSEC_PER_SEC });
 
         if (nanosleep(&ts, &ts) == 0)
                 alarm_handler(SIGVTALRM, NULL);
+        after_sleep_interval(&ts);
 }