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qemu-timer: make qemu_timer_mod_ns() and qemu_timer_del() thread-safe 

Introduce QEMUTimerList->active_timers_lock to protect the linked list
of active timers.  This allows qemu_timer_mod_ns() to be called from any
thread.

Note that vm_clock is not thread-safe and its use of
qemu_clock_has_timers() works fine today but is also not thread-safe.

The purpose of this patch is to eventually let device models set or
cancel timers from a vcpu thread without holding the global mutex.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2013-09-12 11:02:19 +02:00
parent da718ceb17
commit 978f2205c7
2 changed files with 85 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
include/qemu/timer.h
View File

@ -115,6 +115,10 @@ static inline int64_t qemu_clock_get_us(QEMUClockType type)
* Determines whether a clock's default timer list
* has timers attached
*
* Note that this function should not be used when other threads also access
* the timer list. The return value may be outdated by the time it is acted
* upon.
*
* Returns: true if the clock's default timer list
* has timers attached
*/
@ -271,6 +275,10 @@ void timerlist_free(QEMUTimerList *timer_list);
*
* Determine whether a timer list has active timers
*
* Note that this function should not be used when other threads also access
* the timer list. The return value may be outdated by the time it is acted
* upon.
*
* Returns: true if the timer list has timers.
*/
bool timerlist_has_timers(QEMUTimerList *timer_list);
@ -512,6 +520,9 @@ void timer_free(QEMUTimer *ts);
* @ts: the timer
*
* Delete a timer from the active list.
*
* This function is thread-safe but the timer and its timer list must not be
* freed while this function is running.
*/
void timer_del(QEMUTimer *ts);
@ -521,6 +532,9 @@ void timer_del(QEMUTimer *ts);
* @expire_time: the expiry time in nanoseconds
*
* Modify a timer to expire at @expire_time
*
* This function is thread-safe but the timer and its timer list must not be
* freed while this function is running.
*/
void timer_mod_ns(QEMUTimer *ts, int64_t expire_time);
@ -531,6 +545,9 @@ void timer_mod_ns(QEMUTimer *ts, int64_t expire_time);
*
* Modify a timer to expiry at @expire_time, taking into
* account the scale associated with the timer.
*
* This function is thread-safe but the timer and its timer list must not be
* freed while this function is running.
*/
void timer_mod(QEMUTimer *ts, int64_t expire_timer);

87
qemu-timer.c
View File

@ -66,6 +66,7 @@ QEMUClock qemu_clocks[QEMU_CLOCK_MAX];
struct QEMUTimerList {
QEMUClock *clock;
QemuMutex active_timers_lock;
QEMUTimer *active_timers;
QLIST_ENTRY(QEMUTimerList) list;
QEMUTimerListNotifyCB *notify_cb;
@ -101,6 +102,7 @@ QEMUTimerList *timerlist_new(QEMUClockType type,
timer_list->clock = clock;
timer_list->notify_cb = cb;
timer_list->notify_opaque = opaque;
qemu_mutex_init(&timer_list->active_timers_lock);
QLIST_INSERT_HEAD(&clock->timerlists, timer_list, list);
return timer_list;
}
@ -111,6 +113,7 @@ void timerlist_free(QEMUTimerList *timer_list)
if (timer_list->clock) {
QLIST_REMOVE(timer_list, list);
}
qemu_mutex_destroy(&timer_list->active_timers_lock);
g_free(timer_list);
}
@ -163,9 +166,17 @@ bool qemu_clock_has_timers(QEMUClockType type)
bool timerlist_expired(QEMUTimerList *timer_list)
{
return (timer_list->active_timers &&
timer_list->active_timers->expire_time <
qemu_clock_get_ns(timer_list->clock->type));
int64_t expire_time;
qemu_mutex_lock(&timer_list->active_timers_lock);
if (!timer_list->active_timers) {
qemu_mutex_unlock(&timer_list->active_timers_lock);
return false;
}
expire_time = timer_list->active_timers->expire_time;
qemu_mutex_unlock(&timer_list->active_timers_lock);
return expire_time < qemu_clock_get_ns(timer_list->clock->type);
}
bool qemu_clock_expired(QEMUClockType type)
@ -182,13 +193,25 @@ bool qemu_clock_expired(QEMUClockType type)
int64_t timerlist_deadline_ns(QEMUTimerList *timer_list)
{
int64_t delta;
int64_t expire_time;
if (!timer_list->clock->enabled || !timer_list->active_timers) {
if (!timer_list->clock->enabled) {
return -1;
}
delta = timer_list->active_timers->expire_time -
qemu_clock_get_ns(timer_list->clock->type);
/* The active timers list may be modified before the caller uses our return
* value but ->notify_cb() is called when the deadline changes. Therefore
* the caller should notice the change and there is no race condition.
*/
qemu_mutex_lock(&timer_list->active_timers_lock);
if (!timer_list->active_timers) {
qemu_mutex_unlock(&timer_list->active_timers_lock);
return -1;
}
expire_time = timer_list->active_timers->expire_time;
qemu_mutex_unlock(&timer_list->active_timers_lock);
delta = expire_time - qemu_clock_get_ns(timer_list->clock->type);
if (delta <= 0) {
return 0;
@ -296,12 +319,11 @@ void timer_free(QEMUTimer *ts)
g_free(ts);
}
/* stop a timer, but do not dealloc it */
void timer_del(QEMUTimer *ts)
static void timer_del_locked(QEMUTimerList *timer_list, QEMUTimer *ts)
{
QEMUTimer **pt, *t;
pt = &ts->timer_list->active_timers;
pt = &timer_list->active_timers;
for(;;) {
t = *pt;
if (!t)
@ -314,16 +336,28 @@ void timer_del(QEMUTimer *ts)
}
}
/* stop a timer, but do not dealloc it */
void timer_del(QEMUTimer *ts)
{
QEMUTimerList *timer_list = ts->timer_list;
qemu_mutex_lock(&timer_list->active_timers_lock);
timer_del_locked(timer_list, ts);
qemu_mutex_unlock(&timer_list->active_timers_lock);
}
/* modify the current timer so that it will be fired when current_time
>= expire_time. The corresponding callback will be called. */
void timer_mod_ns(QEMUTimer *ts, int64_t expire_time)
{
QEMUTimerList *timer_list = ts->timer_list;
QEMUTimer **pt, *t;
timer_del(ts);
qemu_mutex_lock(&timer_list->active_timers_lock);
timer_del_locked(timer_list, ts);
/* add the timer in the sorted list */
pt = &ts->timer_list->active_timers;
pt = &timer_list->active_timers;
for(;;) {
t = *pt;
if (!timer_expired_ns(t, expire_time)) {
@ -334,12 +368,13 @@ void timer_mod_ns(QEMUTimer *ts, int64_t expire_time)
ts->expire_time = expire_time;
ts->next = *pt;
*pt = ts;
qemu_mutex_unlock(&timer_list->active_timers_lock);
/* Rearm if necessary */
if (pt == &ts->timer_list->active_timers) {
if (pt == &timer_list->active_timers) {
/* Interrupt execution to force deadline recalculation. */
qemu_clock_warp(ts->timer_list->clock->type);
timerlist_notify(ts->timer_list);
qemu_clock_warp(timer_list->clock->type);
timerlist_notify(timer_list);
}
}
@ -350,13 +385,19 @@ void timer_mod(QEMUTimer *ts, int64_t expire_time)
bool timer_pending(QEMUTimer *ts)
{
QEMUTimerList *timer_list = ts->timer_list;
QEMUTimer *t;
for (t = ts->timer_list->active_timers; t != NULL; t = t->next) {
bool found = false;
qemu_mutex_lock(&timer_list->active_timers_lock);
for (t = timer_list->active_timers; t != NULL; t = t->next) {
if (t == ts) {
return true;
found = true;
break;
}
}
return false;
qemu_mutex_unlock(&timer_list->active_timers_lock);
return found;
}
bool timer_expired(QEMUTimer *timer_head, int64_t current_time)
@ -369,23 +410,31 @@ bool timerlist_run_timers(QEMUTimerList *timer_list)
QEMUTimer *ts;
int64_t current_time;
bool progress = false;
QEMUTimerCB *cb;
void *opaque;
if (!timer_list->clock->enabled) {
return progress;
}
current_time = qemu_clock_get_ns(timer_list->clock->type);
for(;;) {
qemu_mutex_lock(&timer_list->active_timers_lock);
ts = timer_list->active_timers;
if (!timer_expired_ns(ts, current_time)) {
qemu_mutex_unlock(&timer_list->active_timers_lock);
break;
}
/* remove timer from the list before calling the callback */
timer_list->active_timers = ts->next;
ts->next = NULL;
cb = ts->cb;
opaque = ts->opaque;
qemu_mutex_unlock(&timer_list->active_timers_lock);
/* run the callback (the timer list can be modified) */
ts->cb(ts->opaque);
cb(opaque);
progress = true;
}
return progress;