[PATCH V2] usbnet: fix race condition caused spinlock bad magic issue

[wangbiao <biao.wang@intel.com>]

From: wang, biao <biao.wang@intel.com>
Date: Mon, 11 Nov 2013 10:23:40 +0800
Subject: [PATCH] usbnet: fix race condition caused spinlock bad magic issue

1, there is race between usbnet_terminate_urbs and usbnet_bh, when
unlink_wakeup used in usbnet_bh, it may be already freed and used by
other function as unlink_wakeup was a local var on stack.
for example:
    cpu 0:                              cpu 1:
                                    usb_suspend_both
                                    ->usbnet_suspend
usbnet_bh                           ->usbnet_terminate_urbs
->__wake_up
->_raw_spin_unlock_irqrestore
->do_raw_spin_unlock
->spin_bug
when usbnet_terminate_urbs complete execution and memory of unlink_wakeup was
used by other function, then usbnet_bh may still use it.

2, for the same reason,dev->wait should be judged again before use it,
as between the judge point(if(dev->wait)) and use point(wakeup(dev->wait)),
the dev->wait may be set NULL by another cpu.

for issue 1, declare  unlink_wakeup in global section instead of on stack.
for issue 2, use a temporary local var to keep the value of dev->wait
in stack and judge it before using.

Signed-off-by: wang, biao <biao.wang@intel.com>
Acked-by: Ingo Molnar <mingo.kernel.org@gmail.com>
Acked-by: Oliver Neukum <oneukum@suse.de>
Acked-by: Zhang, Di <di.zhang@intel.com>
---
 drivers/net/usb/usbnet.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 90a429b..0603ef6 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -86,6 +86,7 @@ static const char driver_name [] = "usbnet";
 
 /* use ethtool to change the level for any given device */
 static int msg_level = -1;
+static DECLARE_WAIT_QUEUE_HEAD(unlink_wakeup);
 module_param (msg_level, int, 0);
 MODULE_PARM_DESC (msg_level, "Override default message level");
 
@@ -761,7 +762,6 @@ EXPORT_SYMBOL_GPL(usbnet_unlink_rx_urbs);
 // precondition: never called in_interrupt
 static void usbnet_terminate_urbs(struct usbnet *dev)
 {
-	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(unlink_wakeup);
 	DECLARE_WAITQUEUE(wait, current);
 	int temp;
 
@@ -1449,7 +1449,9 @@ static void usbnet_bh (unsigned long param)
 	// waiting for all pending urbs to complete?
 	if (dev->wait) {
 		if ((dev->txq.qlen + dev->rxq.qlen + dev->done.qlen) == 0) {
-			wake_up (dev->wait);
+			wait_queue_head_t *wait_d = dev->wait;
+			if (wait_d)
+				wake_up(wait_d);
 		}
 
 	// or are we maybe short a few urbs?
-- 
1.7.0.4