linux-kernel - Re: [syzbot] [sound?] INFO: task hung in snd_card

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Message-ID: <tencent_C01B2E4B191BB0251ABA8BBB47338C9E3508@qq.com>
Date: Wed,  6 Nov 2024 09:37:16 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+73582d08864d8268b6fd@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [sound?] INFO: task hung in snd_card_free

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) {