linux-kernel - [PATCH 3.2 76/94] ALSA: timer: Protect the whole snd_timer

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Date:   Thu, 28 Dec 2017 16:59:12 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.2 76/94] ALSA: timer: Protect the whole snd_timer_close()
 with open race

3.2.97-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

commit 9984d1b5835ca29fc7025186a891ee7398d21cc7 upstream.

In order to make the open/close more robust, widen the register_mutex
protection over the whole snd_timer_close() function.  Also, the close
procedure is slightly shuffled to be in the safer order, as well as a
few code refactoring.

Signed-off-by: Takashi Iwai <tiwai@...e.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 sound/core/timer.c | 48 +++++++++++++++++++++---------------------------
 1 file changed, 21 insertions(+), 27 deletions(-)

--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -326,25 +326,14 @@ int snd_timer_close(struct snd_timer_ins
 	if (snd_BUG_ON(!timeri))
 		return -ENXIO;
 
+	mutex_lock(&register_mutex);
+	list_del(&timeri->open_list);
+
 	/* force to stop the timer */
 	snd_timer_stop(timeri);
 
-	if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) {
-		/* wait, until the active callback is finished */
-		spin_lock_irq(&slave_active_lock);
-		while (timeri->flags & SNDRV_TIMER_IFLG_CALLBACK) {
-			spin_unlock_irq(&slave_active_lock);
-			udelay(10);
-			spin_lock_irq(&slave_active_lock);
-		}
-		spin_unlock_irq(&slave_active_lock);
-		mutex_lock(&register_mutex);
-		list_del(&timeri->open_list);
-		mutex_unlock(&register_mutex);
-	} else {
-		timer = timeri->timer;
-		if (snd_BUG_ON(!timer))
-			goto out;
+	timer = timeri->timer;
+	if (timer) {
 		/* wait, until the active callback is finished */
 		spin_lock_irq(&timer->lock);
 		while (timeri->flags & SNDRV_TIMER_IFLG_CALLBACK) {
@@ -353,11 +342,7 @@ int snd_timer_close(struct snd_timer_ins
 			spin_lock_irq(&timer->lock);
 		}
 		spin_unlock_irq(&timer->lock);
-		mutex_lock(&register_mutex);
-		list_del(&timeri->open_list);
-		if (list_empty(&timer->open_list_head) &&
-		    timer->hw.close)
-			timer->hw.close(timer);
+
 		/* remove slave links */
 		spin_lock_irq(&slave_active_lock);
 		spin_lock(&timer->lock);
@@ -371,15 +356,24 @@ int snd_timer_close(struct snd_timer_ins
 		}
 		spin_unlock(&timer->lock);
 		spin_unlock_irq(&slave_active_lock);
-		mutex_unlock(&register_mutex);
+
+		/* slave doesn't need to release timer resources below */
+		if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE)
+			timer = NULL;
 	}
- out:
+
 	if (timeri->private_free)
 		timeri->private_free(timeri);
 	kfree(timeri->owner);
 	kfree(timeri);
-	if (timer)
+
+	if (timer) {
+		if (list_empty(&timer->open_list_head) && timer->hw.close)
+			timer->hw.close(timer);
 		module_put(timer->module);
+	}
+
+	mutex_unlock(&register_mutex);
 	return 0;
 }