linux-kernel - [PATCH 3.11 062/198] USB: usb_wwan: fix write and suspend race

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Message-Id: <1404379241-8590-63-git-send-email-luis.henriques@canonical.com>
Date:	Thu,  3 Jul 2014 10:18:25 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Johan Hovold <jhovold@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.11 062/198] USB: usb_wwan: fix write and suspend race

3.11.10.13 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <jhovold@...il.com>

commit 170fad9e22df0063eba0701adb966786d7a4ec5a upstream.

Fix race between write() and suspend() which could lead to writes being
dropped (or I/O while suspended) if the device is runtime suspended
while a write request is being processed.

Specifically, suspend() releases the susp_lock after determining the
device is idle but before setting the suspended flag, thus leaving a
window where a concurrent write() can submit an urb.

Fixes: 383cedc3bb43 ("USB: serial: full autosuspend support for the
option driver")

Signed-off-by: Johan Hovold <jhovold@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/usb/serial/usb_wwan.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/usb/serial/usb_wwan.c b/drivers/usb/serial/usb_wwan.c
index 80c16d84156a..ede88f1e09a3 100644
--- a/drivers/usb/serial/usb_wwan.c
+++ b/drivers/usb/serial/usb_wwan.c
@@ -583,20 +583,17 @@ static void stop_read_write_urbs(struct usb_serial *serial)
 int usb_wwan_suspend(struct usb_serial *serial, pm_message_t message)
 {
 	struct usb_wwan_intf_private *intfdata = serial->private;
-	int b;
 
+	spin_lock_irq(&intfdata->susp_lock);
 	if (PMSG_IS_AUTO(message)) {
-		spin_lock_irq(&intfdata->susp_lock);
-		b = intfdata->in_flight;
-		spin_unlock_irq(&intfdata->susp_lock);
-
-		if (b)
+		if (intfdata->in_flight) {
+			spin_unlock_irq(&intfdata->susp_lock);
 			return -EBUSY;
+		}
 	}
-
-	spin_lock_irq(&intfdata->susp_lock);
 	intfdata->suspended = 1;
 	spin_unlock_irq(&intfdata->susp_lock);
+
 	stop_read_write_urbs(serial);
 
 	return 0;
-- 
1.9.1

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