linux-kernel - [PATCH] usb: fix a task hung in snd_card

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Message-ID: <tencent_9E3DBD3732961C37FC4AEC74E3763367E209@qq.com>
Date: Wed,  6 Nov 2024 10:15:49 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+73582d08864d8268b6fd@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	linux-sound@...r.kernel.org,
	perex@...ex.cz,
	syzkaller-bugs@...glegroups.com,
	tiwai@...e.com
Subject: [PATCH] usb: fix a task hung in snd_card_free

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

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

Adjust the USB lock acquisition method to non-blocking in ioctl to avoid
hang when the USB connection is closed.

Reported-and-tested-by: syzbot+73582d08864d8268b6fd@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=73582d08864d8268b6fd
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
 drivers/usb/core/devio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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) {
-- 
2.43.0