[PATCH 02/14] USB: serial: keyspan_pda: fix write deadlock

From: Johan Hovold <johan@kernel.org>
To: linux-usb@vger.kernel.org
Cc: "Ahmed S . Darwish" <a.darwish@linutronix.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, Johan Hovold <johan@kernel.org>,
	stable <stable@vger.kernel.org>
Subject: [PATCH 02/14] USB: serial: keyspan_pda: fix write deadlock
Date: Sun, 25 Oct 2020 18:45:48 +0100	[thread overview]
Message-ID: <20201025174600.27896-3-johan@kernel.org> (raw)
In-Reply-To: <20201025174600.27896-1-johan@kernel.org>

The write() callback can be called in interrupt context (e.g. when used
as a console) so interrupts must be disabled while holding the port lock
to prevent a possible deadlock.

Fixes: e81ee637e4ae ("usb-serial: possible irq lock inversion (PPP vs. usb/serial)")
Fixes: 507ca9bc0476 ("[PATCH] USB: add ability for usb-serial drivers to determine if their write urb is currently being used.")
Cc: stable <stable@vger.kernel.org>     # 2.6.19
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/usb/serial/keyspan_pda.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/serial/keyspan_pda.c b/drivers/usb/serial/keyspan_pda.c
index 2d5ad579475a..17b60e5a9f1f 100644
--- a/drivers/usb/serial/keyspan_pda.c
+++ b/drivers/usb/serial/keyspan_pda.c
@@ -443,6 +443,7 @@ static int keyspan_pda_write(struct tty_struct *tty,
 	int request_unthrottle = 0;
 	int rc = 0;
 	struct keyspan_pda_private *priv;
+	unsigned long flags;
 
 	priv = usb_get_serial_port_data(port);
 	/* guess how much room is left in the device's ring buffer, and if we
@@ -462,13 +463,13 @@ static int keyspan_pda_write(struct tty_struct *tty,
 	   the TX urb is in-flight (wait until it completes)
 	   the device is full (wait until it says there is room)
 	*/
-	spin_lock_bh(&port->lock);
+	spin_lock_irqsave(&port->lock, flags);
 	if (!test_bit(0, &port->write_urbs_free) || priv->tx_throttled) {
-		spin_unlock_bh(&port->lock);
+		spin_unlock_irqrestore(&port->lock, flags);
 		return 0;
 	}
 	clear_bit(0, &port->write_urbs_free);
-	spin_unlock_bh(&port->lock);
+	spin_unlock_irqrestore(&port->lock, flags);
 
 	/* At this point the URB is in our control, nobody else can submit it
 	   again (the only sudden transition was the one from EINPROGRESS to
-- 
2.26.2

