[Qemu-devel] Bug: hpet timer hangs QEMU using icount

[Xin Li <xin.li@rochester.edu>]

Hpet hangs QEMU when icount is present. I don't know if this is a 
universal problem. The cause is that for periodical timers, hpet_timer 
function tries to insert the timer back to the active timers queue, 
using an updated expire time. However, before the update, if the expire 
time is equal to the current time, this updating will be skipped. As a 
result, this timer will be inserted as is and goes off again and again, 
basically traps itself in a infinite loop, preventing any new 
instructions from being executed.

The patch tries to update the timer even when the current time equals 
the old expire time.

Thanks.

-Xin

--- hw/hpet.c   2010-03-01 23:58:08.815931235 -0500
+++ hw/new_hpet.c       2010-03-01 23:55:07.316704119 -0500
@@ -220,10 +220,10 @@

      if (timer_is_periodic(t) && period != 0) {
          if (t->config & HPET_TN_32BIT) {
-            while (hpet_time_after(cur_tick, t->cmp))
+            while (!hpet_time_after(t->cmp, cur_tick))
                  t->cmp = (uint32_t)(t->cmp + t->period);
          } else
-            while (hpet_time_after64(cur_tick, t->cmp))
+            while (!hpet_time_after64(t->cmp, cur_tick))
                  t->cmp += period;

          diff = hpet_calculate_diff(t, cur_tick);