@@ -185,6 +185,12 @@ void qemu_clock_notify(QEMUClockType type);
* @enabled: true to enable, false to disable
*
* Enable or disable a clock
+ * Disabling the clock will wait for related timerlists to stop
+ * executing qemu_run_timers. Thus, this functions should not
+ * be used from the callback of a timer that is based on @clock.
+ * Doing so would cause a deadlock.
+ *
+ * Caller should hold BQL.
*/
void qemu_clock_enable(QEMUClockType type, bool enabled);
@@ -45,6 +45,7 @@
/* timers */
typedef struct QEMUClock {
+ /* We rely on BQL to protect the timerlists */
QLIST_HEAD(, QEMUTimerList) timerlists;
NotifierList reset_notifiers;
@@ -70,6 +71,8 @@ struct QEMUTimerList {
QLIST_ENTRY(QEMUTimerList) list;
QEMUTimerListNotifyCB *notify_cb;
void *notify_opaque;
+ /* light weight method to mark the end of timerlist's running */
+ QemuEvent timers_done_ev;
};
/**
@@ -98,6 +101,7 @@ QEMUTimerList *timerlist_new(QEMUClockType type,
QEMUClock *clock = qemu_clock_ptr(type);
timer_list = g_malloc0(sizeof(QEMUTimerList));
+ qemu_event_init(&timer_list->timers_done_ev, false);
timer_list->clock = clock;
timer_list->notify_cb = cb;
timer_list->notify_opaque = opaque;
@@ -140,13 +144,25 @@ void qemu_clock_notify(QEMUClockType type)
}
}
+/* Disabling the clock will wait for related timerlists to stop
+ * executing qemu_run_timers. Thus, this functions should not
+ * be used from the callback of a timer that is based on @clock.
+ * Doing so would cause a deadlock.
+ *
+ * Caller should hold BQL.
+ */
void qemu_clock_enable(QEMUClockType type, bool enabled)
{
QEMUClock *clock = qemu_clock_ptr(type);
+ QEMUTimerList *tl;
bool old = clock->enabled;
clock->enabled = enabled;
if (enabled && !old) {
qemu_clock_notify(type);
+ } else if (!enabled && old) {
+ QLIST_FOREACH(tl, &clock->timerlists, list) {
+ qemu_event_wait(&tl->timers_done_ev);
+ }
}
}
@@ -373,8 +389,10 @@ bool timerlist_run_timers(QEMUTimerList *timer_list)
QEMUTimer *ts;
int64_t current_time;
bool progress = false;
-
+
+ qemu_event_reset(&timer_list->timers_done_ev);
if (!timer_list->clock->enabled) {
+ qemu_event_set(&timer_list->timers_done_ev);
return progress;
}
@@ -392,6 +410,7 @@ bool timerlist_run_timers(QEMUTimerList *timer_list)
ts->cb(ts->opaque);
progress = true;
}
+ qemu_event_set(&timer_list->timers_done_ev);
return progress;
}
After disabling the QemuClock, we should make sure that no QemuTimers are still in flight. To implement that with light overhead, we resort to QemuEvent. The caller of disabling will wait on QemuEvent of each timerlist. Note, qemu_clock_enable(foo,false) can _not_ be called from timer's cb. And the callers of qemu_clock_enable() should be sync by themselves, not protected by this patch. Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com> --- include/qemu/timer.h | 6 ++++++ qemu-timer.c | 21 ++++++++++++++++++++- 2 files changed, 26 insertions(+), 1 deletion(-)