USB: usb_wwan: fix write and suspend race

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@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/usb/serial/usb_wwan.c b/drivers/usb/serial/usb_wwan.c
index 7ccff6c..bb2a713 100644 (file)
--- a/drivers/usb/serial/usb_wwan.c
+++ b/drivers/usb/serial/usb_wwan.c
@@ -647,22 +647,19 @@ EXPORT_SYMBOL(usb_wwan_release);
 int usb_wwan_suspend(struct usb_serial *serial, pm_message_t message)
 {
        struct usb_wwan_intf_private *intfdata = serial->private;
-       int b;
 
        dbg("%s entered", __func__);
 
+       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;