[PATCH 3.16 333/366] ALSA: timer: Call notifier in the same spinlock

Ben Hutchings
2018-10-14T23:11:54Z

From: Takashi Iwai <tiwai@suse.de>

commit f65e0d299807d8a11812845c972493c3f9a18e10 upstream.

snd_timer_notify1() is called outside the spinlock and it retakes the
lock after the unlock. This is rather racy, and it's safer to move
snd_timer_notify() call inside the main spinlock.

The patch also contains a slight refactoring / cleanup of the code.
Now all start/stop/continue/pause look more symmetric and a bit better
readable.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
[bwh: Backported to 3.16:
- Fix up another use of "event" in _snd_timer_stop()
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -347,8 +347,6 @@ int snd_timer_open(struct snd_timer_inst
return err;
}

-static int _snd_timer_stop(struct snd_timer_instance *timeri, int event);
-
/*
* close a timer instance
* call this with register_mutex down.
@@ -445,7 +443,6 @@ unsigned long snd_timer_resolution(struc
static void snd_timer_notify1(struct snd_timer_instance *ti, int event)
{
struct snd_timer *timer;
- unsigned long flags;
unsigned long resolution = 0;
struct snd_timer_instance *ts;
struct timespec tstamp;
@@ -469,34 +466,66 @@ static void snd_timer_notify1(struct snd
return;
if (timer->hw.flags & SNDRV_TIMER_HW_SLAVE)
return;
- spin_lock_irqsave(&timer->lock, flags);
list_for_each_entry(ts, &ti->slave_active_head, active_list)
if (ts->ccallback)
ts->ccallback(ts, event + 100, &tstamp, resolution);
- spin_unlock_irqrestore(&timer->lock, flags);
}

-static int snd_timer_start1(struct snd_timer *timer, struct snd_timer_instance *timeri,
- unsigned long sticks)
+/* start/continue a master timer */
+static int snd_timer_start1(struct snd_timer_instance *timeri,
+ bool start, unsigned long ticks)
{
+ struct snd_timer *timer;
+ int result;
+ unsigned long flags;
+
+ timer = timeri->timer;
+ if (!timer)
+ return -EINVAL;
+
+ spin_lock_irqsave(&timer->lock, flags);
+ if (timer->card && timer->card->shutdown) {
+ result = -ENODEV;
+ goto unlock;
+ }
+ if (timeri->flags & (SNDRV_TIMER_IFLG_RUNNING |
+ SNDRV_TIMER_IFLG_START)) {
+ result = -EBUSY;
+ goto unlock;
+ }
+
+ if (start)
+ timeri->ticks = timeri->cticks = ticks;
+ else if (!timeri->cticks)
+ timeri->cticks = 1;
+ timeri->pticks = 0;
+
list_move_tail(&timeri->active_list, &timer->active_list_head);
if (timer->running) {
if (timer->hw.flags & SNDRV_TIMER_HW_SLAVE)
goto __start_now;
timer->flags |= SNDRV_TIMER_FLG_RESCHED;
timeri->flags |= SNDRV_TIMER_IFLG_START;
- return 1; /* delayed start */
+ result = 1; /* delayed start */
} else {
- timer->sticks = sticks;
+ if (start)
+ timer->sticks = ticks;
timer->hw.start(timer);
__start_now:
timer->running++;
timeri->flags |= SNDRV_TIMER_IFLG_RUNNING;
- return 0;
+ result = 0;
}
+ snd_timer_notify1(timeri, start ? SNDRV_TIMER_EVENT_START :
+ SNDRV_TIMER_EVENT_CONTINUE);
+ unlock:
+ spin_unlock_irqrestore(&timer->lock, flags);
+ return result;
}

-static int snd_timer_start_slave(struct snd_timer_instance *timeri)
+/* start/continue a slave timer */
+static int snd_timer_start_slave(struct snd_timer_instance *timeri,
+ bool start)
{
unsigned long flags;

@@ -510,88 +539,37 @@ static int snd_timer_start_slave(struct
spin_lock(&timeri->timer->lock);
list_add_tail(&timeri->active_list,
&timeri->master->slave_active_head);
+ snd_timer_notify1(timeri, start ? SNDRV_TIMER_EVENT_START :
+ SNDRV_TIMER_EVENT_CONTINUE);
spin_unlock(&timeri->timer->lock);
}
spin_unlock_irqrestore(&slave_active_lock, flags);
return 1; /* delayed start */
}

-/*
- * start the timer instance
- */
-int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks)
-{
- struct snd_timer *timer;
- int result = -EINVAL;
- unsigned long flags;
-
- if (timeri == NULL || ticks < 1)
- return -EINVAL;
- if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) {
- result = snd_timer_start_slave(timeri);
- if (result >= 0)
- snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START);
- return result;
- }
- timer = timeri->timer;
- if (timer == NULL)
- return -EINVAL;
- if (timer->card && timer->card->shutdown)
- return -ENODEV;
- spin_lock_irqsave(&timer->lock, flags);
- if (timeri->flags & (SNDRV_TIMER_IFLG_RUNNING |
- SNDRV_TIMER_IFLG_START)) {
- result = -EBUSY;
- goto unlock;
- }
- timeri->ticks = timeri->cticks = ticks;
- timeri->pticks = 0;
- result = snd_timer_start1(timer, timeri, ticks);
- unlock:
- spin_unlock_irqrestore(&timer->lock, flags);
- if (result >= 0)
- snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START);
- return result;
-}
-
-static int _snd_timer_stop(struct snd_timer_instance *timeri, int event)
+/* stop/pause a master timer */
+static int snd_timer_stop1(struct snd_timer_instance *timeri, bool stop)
{
struct snd_timer *timer;
+ int result = 0;
unsigned long flags;

- if (snd_BUG_ON(!timeri))
- return -ENXIO;
-
- if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) {
- spin_lock_irqsave(&slave_active_lock, flags);
- if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) {
- spin_unlock_irqrestore(&slave_active_lock, flags);
- return -EBUSY;
- }
- if (timeri->timer)
- spin_lock(&timeri->timer->lock);
- timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
- list_del_init(&timeri->ack_list);
- list_del_init(&timeri->active_list);
- if (timeri->timer)
- spin_unlock(&timeri->timer->lock);
- spin_unlock_irqrestore(&slave_active_lock, flags);
- goto __end;
- }
timer = timeri->timer;
if (!timer)
return -EINVAL;
spin_lock_irqsave(&timer->lock, flags);
if (!(timeri->flags & (SNDRV_TIMER_IFLG_RUNNING |
SNDRV_TIMER_IFLG_START))) {
- spin_unlock_irqrestore(&timer->lock, flags);
- return -EBUSY;
+ result = -EBUSY;
+ goto unlock;
}
list_del_init(&timeri->ack_list);
list_del_init(&timeri->active_list);
- if (timer->card && timer->card->shutdown) {
- spin_unlock_irqrestore(&timer->lock, flags);
- return 0;
+ if (timer->card && timer->card->shutdown)
+ goto unlock;
+ if (stop) {
+ timeri->cticks = timeri->ticks;
+ timeri->pticks = 0;
}
if ((timeri->flags & SNDRV_TIMER_IFLG_RUNNING) &&
!(--timer->running)) {
@@ -606,39 +584,64 @@ static int _snd_timer_stop(struct snd_ti
}
}
timeri->flags &= ~(SNDRV_TIMER_IFLG_RUNNING | SNDRV_TIMER_IFLG_START);
- if (event == SNDRV_TIMER_EVENT_STOP)
+ if (stop)
timeri->flags &= ~SNDRV_TIMER_IFLG_PAUSED;
else
timeri->flags |= SNDRV_TIMER_IFLG_PAUSED;
+ snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP :
+ SNDRV_TIMER_EVENT_CONTINUE);
+ unlock:
spin_unlock_irqrestore(&timer->lock, flags);
- __end:
- if (event != SNDRV_TIMER_EVENT_RESOLUTION)
- snd_timer_notify1(timeri, event);
+ return result;
+}
+
+/* stop/pause a slave timer */
+static int snd_timer_stop_slave(struct snd_timer_instance *timeri, bool stop)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&slave_active_lock, flags);
+ if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) {
+ spin_unlock_irqrestore(&slave_active_lock, flags);
+ return -EBUSY;
+ }
+ timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
+ if (timeri->timer) {
+ spin_lock(&timeri->timer->lock);
+ list_del_init(&timeri->ack_list);
+ list_del_init(&timeri->active_list);
+ snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP :
+ SNDRV_TIMER_EVENT_CONTINUE);
+ spin_unlock(&timeri->timer->lock);
+ }
+ spin_unlock_irqrestore(&slave_active_lock, flags);
return 0;
}

/*
+ * start the timer instance
+ */
+int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks)
+{
+ if (timeri == NULL || ticks < 1)
+ return -EINVAL;
+ if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE)
+ return snd_timer_start_slave(timeri, true);
+ else
+ return snd_timer_start1(timeri, true, ticks);
+}
+
+/*
* stop the timer instance.
*
* do not call this from the timer callback!
*/
int snd_timer_stop(struct snd_timer_instance *timeri)
{
- struct snd_timer *timer;
- unsigned long flags;
- int err;
-
- err = _snd_timer_stop(timeri, SNDRV_TIMER_EVENT_STOP);
- if (err < 0)
- return err;
- timer = timeri->timer;
- if (!timer)
- return -EINVAL;
- spin_lock_irqsave(&timer->lock, flags);
- timeri->cticks = timeri->ticks;
- timeri->pticks = 0;
- spin_unlock_irqrestore(&timer->lock, flags);
- return 0;
+ if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE)
+ return snd_timer_stop_slave(timeri, true);
+ else
+ return snd_timer_stop1(timeri, true);
}

/*
@@ -646,36 +649,14 @@ int snd_timer_stop(struct snd_timer_inst
*/
int snd_timer_continue(struct snd_timer_instance *timeri)
{
- struct snd_timer *timer;
- int result = -EINVAL;
- unsigned long flags;
-
- if (timeri == NULL)
- return result;
/* timer can continue only after pause */
if (!(timeri->flags & SNDRV_TIMER_IFLG_PAUSED))
return -EINVAL;

if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE)
- return snd_timer_start_slave(timeri);
- timer = timeri->timer;
- if (! timer)
- return -EINVAL;
- if (timer->card && timer->card->shutdown)
- return -ENODEV;
- spin_lock_irqsave(&timer->lock, flags);
- if (timeri->flags & SNDRV_TIMER_IFLG_RUNNING) {
- result = -EBUSY;
- goto unlock;
- }
- if (!timeri->cticks)
- timeri->cticks = 1;
- timeri->pticks = 0;
- result = snd_timer_start1(timer, timeri, timer->sticks);
- unlock:
- spin_unlock_irqrestore(&timer->lock, flags);
- snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_CONTINUE);
- return result;
+ return snd_timer_start_slave(timeri, false);
+ else
+ return snd_timer_start1(timeri, false, 0);
}

/*
@@ -683,7 +664,10 @@ int snd_timer_continue(struct snd_timer_
*/
int snd_timer_pause(struct snd_timer_instance * timeri)
{
- return _snd_timer_stop(timeri, SNDRV_TIMER_EVENT_PAUSE);
+ if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE)
+ return snd_timer_stop_slave(timeri, false);
+ else
+ return snd_timer_stop1(timeri, false);
}

/*