The user timer tu->qused counter may go to a negative value when
multiple concurrent reads are performed since both the check and the
decrement of tu->qused are done in two individual locked contexts.
This results in bogus read outs, and the endless loop in the
user-space side.
The fix is to move the decrement of the tu->qused counter into the
same spinlock context as the zero-check of the counter.
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
sound/core/timer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/sound/core/timer.c b/sound/core/timer.c
index e722022d325d..9a6157ea6881 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1955,6 +1955,7 @@ 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) {
@@ -1968,7 +1969,6 @@ 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;
--
2.9.0
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