@@ -43,6 +43,7 @@
#define SNDRV_TIMER_IFLG_START 0x00000004
#define SNDRV_TIMER_IFLG_AUTO 0x00000008 /* auto restart */
#define SNDRV_TIMER_IFLG_FAST 0x00000010 /* fast callback (do not use tasklet) */
+#define SNDRV_TIMER_IFLG_CALLBACK 0x00000020 /* timer callback is active */
#define SNDRV_TIMER_IFLG_EXCLUSIVE 0x00000040 /* exclusive owner - no more instances */
#define SNDRV_TIMER_IFLG_EARLY_EVENT 0x00000080 /* write early event to the poll queue */
@@ -372,7 +372,7 @@ static int snd_timer_close_locked(struct snd_timer_instance *timeri)
timer->num_instances--;
/* wait, until the active callback is finished */
spin_lock_irq(&timer->lock);
- while (!list_empty(&timeri->ack_list)) {
+ while (timeri->flags & SNDRV_TIMER_IFLG_CALLBACK) {
spin_unlock_irq(&timer->lock);
udelay(10);
spin_lock_irq(&timer->lock);
@@ -748,19 +748,20 @@ static void snd_timer_process_callbacks(struct snd_timer *timer,
ti = list_first_entry(head, struct snd_timer_instance,
ack_list);
+ /* remove from ack_list and make empty */
+ list_del_init(&ti->ack_list);
+
if (!(ti->flags & SNDRV_TIMER_IFLG_DEAD)) {
ticks = ti->pticks;
ti->pticks = 0;
resolution = ti->resolution;
-
+ ti->flags |= SNDRV_TIMER_IFLG_CALLBACK;
spin_unlock(&timer->lock);
if (ti->callback)
ti->callback(ti, resolution, ticks);
spin_lock(&timer->lock);
+ ti->flags &= ~SNDRV_TIMER_IFLG_CALLBACK;
}
-
- /* remove from ack_list and make empty */
- list_del_init(&ti->ack_list);
}
}
This is essentially a revert of the commit a7588c896b05 ("ALSA: timer: Check ack_list emptiness instead of bit flag"). The intended change by the commit turns out to be insufficient, as snd_timer_close*() always calls snd_timer_stop() that deletes the ack_list beforehand. In theory, we can change the behavior of snd_timer_stop() to sync the pending ack_list, but this will become a deadlock for the callback like sequencer that calls again snd_timer_stop() from itself. So, reverting the change is a more straightforward solution. Fixes: a7588c896b05 ("ALSA: timer: Check ack_list emptiness instead of bit flag") Reported-by: syzbot+58813d77154713f4de15@syzkaller.appspotmail.com Signed-off-by: Takashi Iwai <tiwai@suse.de> --- include/sound/timer.h | 1 + sound/core/timer.c | 11 ++++++----- 2 files changed, 7 insertions(+), 5 deletions(-)