[RFC 4/7] CDC-WDM: fix race reporting errors in flush

[Oliver Neukum <oneukum@suse.com>]

In case a race was lost and multiple fds used,
an error could be reported multiple times. To fix
this a spinlock must be taken.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/class/cdc-wdm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index eee19532e67e..930000b1d43b 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -610,10 +610,14 @@ static int wdm_flush(struct file *file, fl_owner_t id)
 		return -EIO;
 	if (rv < 0)
 		return -EINTR;
+
+	spin_lock_irq(&desc->iuspin);
 	rv = desc->werr;
+	desc->werr = 0;
+	spin_unlock_irq(&desc->iuspin);
+
 	if (rv < 0)
-		dev_err(&desc->intf->dev, "Error in flush path: %d\n",
-			rv);
+		dev_err(&desc->intf->dev, "Error in flush path: %d\n", rv);
 
 	return usb_translate_errors(rv);
 }
-- 
2.16.4