ALSA: timer: Fix negative queue usage by racy accesses

[firefly-linux-kernel-4.4.55.git] / sound / core / timer.c

diff --git a/sound/core/timer.c b/sound/core/timer.c
index b982d1b089bd90ff44267f528dff8690d76ad4db..7c6155f5865b8a4173aff59d74e133ac96b31331 100644 (file)
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1961,6 +1961,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
 
                qhead = tu->qhead++;
                tu->qhead %= tu->queue_size;
+               tu->qused--;
                spin_unlock_irq(&tu->qlock);
 
                if (tu->tread) {
@@ -1974,7 +1975,6 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
                }
 
                spin_lock_irq(&tu->qlock);
-               tu->qused--;
                if (err < 0)
                        goto _error;
                result += unit;