[RFC 1/7] CDC-WDM: fix hangs in flush() in multithreaded cases

[Oliver Neukum <oneukum@suse.com>]

In a multithreaded scenario an arbitrary number of threads
can be in wdm_write() and in wdm_flush(). Hence whenever
WDM_IN_USE is reset, all possible waiters need to be notified.
This is true whether this is due to IO completing or
to an error starting IO.

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/class/cdc-wdm.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index e3db6fbeadef..adb3fc307083 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -151,7 +151,7 @@ static void wdm_out_callback(struct urb *urb)
 	kfree(desc->outbuf);
 	desc->outbuf = NULL;
 	clear_bit(WDM_IN_USE, &desc->flags);
-	wake_up(&desc->wait);
+	wake_up_all(&desc->wait);
 }
 
 static void wdm_in_callback(struct urb *urb)
@@ -424,6 +424,7 @@ static ssize_t wdm_write
 	if (rv < 0) {
 		desc->outbuf = NULL;
 		clear_bit(WDM_IN_USE, &desc->flags);
+		wake_up_all(&desc->wait); /* for flush() */
 		dev_err(&desc->intf->dev, "Tx URB error: %d\n", rv);
 		rv = usb_translate_errors(rv);
 		goto out_free_mem_pm;
@@ -586,6 +587,7 @@ static ssize_t wdm_read
 static int wdm_flush(struct file *file, fl_owner_t id)
 {
 	struct wdm_device *desc = file->private_data;
+	int rv;
 
 	wait_event(desc->wait,
 			/*
@@ -600,11 +602,12 @@ static int wdm_flush(struct file *file, fl_owner_t id)
 	/* cannot dereference desc->intf if WDM_DISCONNECTING */
 	if (test_bit(WDM_DISCONNECTING, &desc->flags))
 		return -ENODEV;
-	if (desc->werr < 0)
+	rv = desc->werr;
+	if (rv < 0)
 		dev_err(&desc->intf->dev, "Error in flush path: %d\n",
-			desc->werr);
+			rv);
 
-	return usb_translate_errors(desc->werr);
+	return usb_translate_errors(rv);
 }
 
 static __poll_t wdm_poll(struct file *file, struct poll_table_struct *wait)
-- 
2.16.4