Re: [syzbot] [sound?] INFO: task hung in snd_card_free

[Edward Adam Davis]

1. snd ctrl will add card_dev ref count and can't call close to dec it,
   it is waiting for 2 to release usb dev lock.

2. usb dev lock has been locked by hung task (here is usb_disconnect), it waiting 1
   to exit and release card_dev.

#syz test

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 3beb6a862e80..dd037dc4cb37 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -2605,7 +2605,8 @@ static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
 	if (!(file->f_mode & FMODE_WRITE))
 		return -EPERM;
 
-	usb_lock_device(dev);
+	if (!usb_trylock_device(dev))
+		return -EBUSY;
 
 	/* Reap operations are allowed even after disconnection */
 	switch (cmd) {