diff --git a/include/qemu/timer.h b/include/qemu/timer.h index 016e29ae95..1254ef729e 100644 --- a/include/qemu/timer.h +++ b/include/qemu/timer.h @@ -189,6 +189,12 @@ 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); diff --git a/qemu-timer.c b/qemu-timer.c index 6b62e88669..2b533da2c7 100644 --- a/qemu-timer.c +++ b/qemu-timer.c @@ -45,6 +45,7 @@ /* timers */ typedef struct QEMUClock { + /* We rely on BQL to protect the timerlists */ QLIST_HEAD(, QEMUTimerList) timerlists; NotifierList reset_notifiers; @@ -71,6 +72,9 @@ struct QEMUTimerList { QLIST_ENTRY(QEMUTimerList) list; QEMUTimerListNotifyCB *notify_cb; void *notify_opaque; + + /* lightweight method to mark the end of timerlist's running */ + QemuEvent timers_done_ev; }; /** @@ -99,6 +103,7 @@ 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; @@ -143,13 +148,25 @@ 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); + } } } @@ -403,8 +420,9 @@ bool timerlist_run_timers(QEMUTimerList *timer_list) QEMUTimerCB *cb; void *opaque; + qemu_event_reset(&timer_list->timers_done_ev); if (!timer_list->clock->enabled) { - return progress; + goto out; } current_time = qemu_clock_get_ns(timer_list->clock->type); @@ -428,6 +446,9 @@ bool timerlist_run_timers(QEMUTimerList *timer_list) cb(opaque); progress = true; } + +out: + qemu_event_set(&timer_list->timers_done_ev); return progress; }