On Aug 05 2013, Liu Ping Fan wrote:
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 pingf...@linux.vnet.ibm.com
---
include/qemu/timer.h | 1 +
qemu-timer.c | 11 +++
2 files changed, 12 insertions(+)
diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index 1363316..ca09ba2 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -85,6 +85,7 @@ int64_t timerlistgroup_deadline_ns(QEMUTimerListGroup tlg);
int qemu_timeout_ns_to_ms(int64_t ns);
int qemu_poll_ns(GPollFD *fds, uint nfds, int64_t timeout);
+/* The disable of clock can not be called in timer's cb */
See below for a more verbose version of the comment. For
now leave it only in the .c file, we should add comments to
all of timer.h.
void qemu_clock_enable(QEMUClock *clock, bool enabled);
void qemu_clock_warp(QEMUClock *clock);
diff --git a/qemu-timer.c b/qemu-timer.c
index ebe7597..5828107 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -71,6 +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 ev;
};
struct QEMUTimer {
@@ -92,6 +94,7 @@ static QEMUTimerList *timerlist_new_from_clock(QEMUClock
*clock)
QEMUTimerList *tl;
tl = g_malloc0(sizeof(QEMUTimerList));
+qemu_event_init(tl-ev, false);
The event should start as set, since set means not inside
qemu_run_timers.
tl-clock = clock;
QLIST_INSERT_HEAD(clock-timerlists, tl, list);
return tl;
@@ -145,12 +148,18 @@ void qemu_clock_notify(QEMUClock *clock)
}
}
+/* The disable of clock can _not_ be called from timer's cb */
/* 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.
*/
void qemu_clock_enable(QEMUClock *clock, bool enabled)
{
+QEMUTimerList *tl;
bool old = clock-enabled;
clock-enabled = enabled;
if (enabled !old) {
qemu_clock_notify(clock);
+} else if (!enabled old) {
+QLIST_FOREACH(tl, clock-timerlists, list) {
+qemu_event_wait(tl-ev);
+}
}
}
@@ -419,6 +428,7 @@ bool timerlist_run_timers(QEMUTimerList *tl)
}
current_time = qemu_get_clock_ns(tl-clock);
+qemu_event_reset(tl-ev);
Race condition here. You need to test clock-enabled while the
event is reset. Otherwise you get:
-
thread 1 is runningthread 2 is running
qemu_clock_enable(foo, false) qemu_run_timers(tl);
-
** event is initially set **
if (!clock-enabled) return;
clock-enabled = false;
qemu_event_wait(tl-ev);
return;
qemu_event_reset(tl-ev);
invokes callback
qemu_event_set(tl-ev);
-
violating the invariant that no callbacks are invoked after the return from
qemu_clock_enable(foo, false).
Paolo
for(;;) {
ts = tl-active_timers;
if (!qemu_timer_expired_ns(ts, current_time)) {
@@ -432,6 +442,7 @@ bool timerlist_run_timers(QEMUTimerList *tl)
ts-cb(ts-opaque);
progress = true;
}
+qemu_event_set(tl-ev);
return progress;
}
--
1.8.1.4
