[PATCH 2/2] ALSA: timer: Introduce stop_sync op

[Takashi Iwai]

So far, the stop callback is invoked only in the atomic way, and it
couldn't sync with the actual stop of the backend.  This ended up
leaving the possible race opened against the running timer handler.

In this patch, a new op, stop_sync, is introduced to snd_timer
object.  This is called at the end of stop action so that the backend
can synchronize with the proper timer deletion.  As an example, both
systimer and hrtimer backends now call del_timer_sync() and
hrtimer_cancel() there for guaranteeing the termination of the pending
interrupt.

Note that the callback is called outside the timer lock so that it
won't lead to ABBA deadlock.

Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
 include/sound/timer.h |  1 +
 sound/core/hrtimer.c  |  9 ++++++++-
 sound/core/timer.c    | 19 ++++++++++++++-----
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/include/sound/timer.h b/include/sound/timer.h
index 6ca6ed4169da..42dee1244b02 100644
--- a/include/sound/timer.h
+++ b/include/sound/timer.h
@@ -75,6 +75,7 @@ struct snd_timer_hardware {
 	unsigned long (*c_resolution) (struct snd_timer * timer);
 	int (*start) (struct snd_timer * timer);
 	int (*stop) (struct snd_timer * timer);
+	int (*stop_sync) (struct snd_timer * timer);
 	int (*set_period) (struct snd_timer * timer, unsigned long period_num, unsigned long period_den);
 	int (*precise_resolution) (struct snd_timer * timer, unsigned long *num, unsigned long *den);
 };
diff --git a/sound/core/hrtimer.c b/sound/core/hrtimer.c
index 79762444bc79..0e4245c6600a 100644
--- a/sound/core/hrtimer.c
+++ b/sound/core/hrtimer.c
@@ -83,7 +83,6 @@ static int snd_hrtimer_close(struct snd_timer *t)
 	struct snd_hrtimer *stime = t->private_data;
 
 	if (stime) {
-		hrtimer_cancel(&stime->hrt);
 		kfree(stime);
 		t->private_data = NULL;
 	}
@@ -110,12 +109,20 @@ static int snd_hrtimer_stop(struct snd_timer *t)
 	return 0;
 }
 
+static int snd_hrtimer_stop_sync(struct snd_timer *t)
+{
+	struct snd_hrtimer *stime = t->private_data;
+	hrtimer_cancel(&stime->hrt);
+	return 0;
+}
+
 static struct snd_timer_hardware hrtimer_hw = {
 	.flags =	SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_TASKLET,
 	.open =		snd_hrtimer_open,
 	.close =	snd_hrtimer_close,
 	.start =	snd_hrtimer_start,
 	.stop =		snd_hrtimer_stop,
+	.stop_sync =	snd_hrtimer_stop_sync,
 };
 
 /*
diff --git a/sound/core/timer.c b/sound/core/timer.c
index c653c409d74d..5bdb6d3b59af 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -358,8 +358,12 @@ int snd_timer_close(struct snd_timer_instance *timeri)
 	kfree(timeri);
 
 	if (timer) {
-		if (list_empty(&timer->open_list_head) && timer->hw.close)
-			timer->hw.close(timer);
+		if (list_empty(&timer->open_list_head)) {
+			if (timer->hw.stop_sync)
+				timer->hw.stop_sync(timer);
+			if (timer->hw.close)
+				timer->hw.close(timer);
+		}
 		/* release a card refcount for safe disconnection */
 		if (timer->card)
 			put_device(&timer->card->card_dev);
@@ -496,6 +500,7 @@ static int snd_timer_stop1(struct snd_timer_instance *timeri, bool stop)
 {
 	struct snd_timer *timer;
 	int result = 0;
+	bool sync = false;
 	unsigned long flags;
 
 	timer = timeri->timer;
@@ -518,12 +523,14 @@ static int snd_timer_stop1(struct snd_timer_instance *timeri, bool stop)
 	if ((timeri->flags & SNDRV_TIMER_IFLG_RUNNING) &&
 	    !(--timer->running)) {
 		timer->hw.stop(timer);
+		sync = true;
 		if (timer->flags & SNDRV_TIMER_FLG_RESCHED) {
 			timer->flags &= ~SNDRV_TIMER_FLG_RESCHED;
 			snd_timer_reschedule(timer, 0);
 			if (timer->flags & SNDRV_TIMER_FLG_CHANGE) {
 				timer->flags &= ~SNDRV_TIMER_FLG_CHANGE;
 				timer->hw.start(timer);
+				sync = false;
 			}
 		}
 	}
@@ -532,6 +539,8 @@ static int snd_timer_stop1(struct snd_timer_instance *timeri, bool stop)
 			  SNDRV_TIMER_EVENT_CONTINUE);
  unlock:
 	spin_unlock_irqrestore(&timer->lock, flags);
+	if (sync && timer->hw.stop_sync)
+		timer->hw.stop_sync(timer);
 	return result;
 }
 
@@ -1052,7 +1061,7 @@ static int snd_timer_s_stop(struct snd_timer * timer)
 	return 0;
 }
 
-static int snd_timer_s_close(struct snd_timer *timer)
+static int snd_timer_s_stop_sync(struct snd_timer *timer)
 {
 	struct snd_timer_system_private *priv;
 
@@ -1066,9 +1075,9 @@ static struct snd_timer_hardware snd_timer_system =
 	.flags =	SNDRV_TIMER_HW_FIRST | SNDRV_TIMER_HW_TASKLET,
 	.resolution =	1000000000L / HZ,
 	.ticks =	10000000L,
-	.close =	snd_timer_s_close,
 	.start =	snd_timer_s_start,
-	.stop =		snd_timer_s_stop
+	.stop =		snd_timer_s_stop,
+	.stop_sync =	snd_timer_s_stop_sync,
 };
 
 static void snd_timer_free_system(struct snd_timer *timer)
-- 
2.8.1


--Multipart_Sun_Apr_24_18:16:12_2016-1--