[PATCH 3.2 031/125] USB: usb_wwan: fix write and suspend race

From: Ben Hutchings
Date: Tue Jul 08 2014 - 15:16:36 EST

3.2.61-rc1 review patch. If anyone has any objections, please let me know.


From: Johan Hovold <jhovold@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
drivers/usb/serial/usb_wwan.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)

--- 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;

return 0;

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