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@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- 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;