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ALSA: timer: Revert active callback sync check at close 

This is essentially a revert of the commit a7588c896b ("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: a7588c896b ("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>
This commit is contained in:
Takashi Iwai 2019-04-09 12:25:32 +02:00
parent 4b81dad109
commit df55531b8b
2 changed files with 7 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/sound/timer.h
View File

@ -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 */

11
sound/core/timer.c
View File

@ -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);
}
}