ALSA: control: Use deferred fasync helper

For avoiding the potential deadlock via kill_fasync() call, use the
new fasync helpers to defer the invocation from the control API.  Note
that it's merely a workaround.

Another note: although we haven't received reports about the deadlock
with the control API, the deadlock is still potentially possible, and
it's better to align the behavior with other core APIs (PCM and
timer); so let's move altogether.

Link: https://lore.kernel.org/r/20220728125945.29533-5-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/include/sound/control.h b/include/sound/control.h
index fcd3cce673ec396a6905ed57e5eaf8e516aa71a3..eae443ba79ba5522c29ca7e1c4e0362e6f26889e 100644 (file)
--- a/include/sound/control.h
+++ b/include/sound/control.h
@@ -109,7 +109,7 @@ struct snd_ctl_file {
        int preferred_subdevice[SND_CTL_SUBDEV_ITEMS];
        wait_queue_head_t change_sleep;
        spinlock_t read_lock;
-       struct fasync_struct *fasync;
+       struct snd_fasync *fasync;
        int subscribed;                 /* read interface is activated */
        struct list_head events;        /* waiting events for read */
 };

diff --git a/sound/core/control.c b/sound/core/control.c
index 4dba3a342458f2ff43497ba5da45ad617c6345e3..f3e893715369f0c759bca83e1184cff63e075398 100644 (file)
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -127,6 +127,7 @@ static int snd_ctl_release(struct inode *inode, struct file *file)
                        if (control->vd[idx].owner == ctl)
                                control->vd[idx].owner = NULL;
        up_write(&card->controls_rwsem);
+       snd_fasync_free(ctl->fasync);
        snd_ctl_empty_read_queue(ctl);
        put_pid(ctl->pid);
        kfree(ctl);
@@ -181,7 +182,7 @@ void snd_ctl_notify(struct snd_card *card, unsigned int mask,
        _found:
                wake_up(&ctl->change_sleep);
                spin_unlock(&ctl->read_lock);
-               kill_fasync(&ctl->fasync, SIGIO, POLL_IN);
+               snd_kill_fasync(ctl->fasync, SIGIO, POLL_IN);
        }
        read_unlock_irqrestore(&card->ctl_files_rwlock, flags);
 }
@@ -2134,7 +2135,7 @@ static int snd_ctl_fasync(int fd, struct file * file, int on)
        struct snd_ctl_file *ctl;
 
        ctl = file->private_data;
-       return fasync_helper(fd, file, on, &ctl->fasync);
+       return snd_fasync_helper(fd, file, on, &ctl->fasync);
 }
 
 /* return the preferred subdevice number if already assigned;
@@ -2302,7 +2303,7 @@ static int snd_ctl_dev_disconnect(struct snd_device *device)
        read_lock_irqsave(&card->ctl_files_rwlock, flags);
        list_for_each_entry(ctl, &card->ctl_files, list) {
                wake_up(&ctl->change_sleep);
-               kill_fasync(&ctl->fasync, SIGIO, POLL_ERR);
+               snd_kill_fasync(ctl->fasync, SIGIO, POLL_ERR);
        }
        read_unlock_irqrestore(&card->ctl_files_rwlock, flags);