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Commit df55531b authored by Takashi Iwai's avatar Takashi Iwai
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ALSA: timer: Revert active callback sync check at close 



This is essentially a revert of the commit a7588c89 ("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: a7588c89 ("ALSA: timer: Check ack_list emptiness instead of bit flag")
Reported-by: default avatar <syzbot+58813d77154713f4de15@syzkaller.appspotmail.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 4b81dad1

include/sound/timer.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */

sound/core/timer.c

+6 −5
Original line number Diff line number Diff line
@@ -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);

	}

}