4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Takashi Iwai <ti...@suse.de>
commit 3fa6993fef634e05d200d141a85df0b044572364 upstream.
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.
Signed-off-by: Takashi Iwai <ti...@suse.de>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
sound/core/timer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1961,6 +1961,7 @@ static ssize_t snd_timer_user_read(struc
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(struc
}
spin_lock_irq(&tu->qlock);
- tu->qused--;
if (err < 0)
goto _error;
result += unit;
