[PATCH AUTOSEL 5.15 21/28] ALSA: control: Use deferred fasync helper

[Sasha Levin]

From: Takashi Iwai <tiwai@xxxxxxx>

[ Upstream commit 4a971e84a7ae10a38d875cd2d4e487c8d1682ca3 ]

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@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/sound/control.h | 2 +-
 sound/core/control.c    | 7 ++++---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/sound/control.h b/include/sound/control.h
index 985c51a8fb74..a1fc7e0a47d9 100644
--- 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 a25c0d64d104..f66fe4be30d3 100644
--- 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);
 }
@@ -2002,7 +2003,7 @@ 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;
@@ -2170,7 +2171,7 @@ 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);
 
-- 
2.35.1