[PATCH V3] usbnet: fix race condition caused spinlock bad magic issue

[PATCH V3] usbnet: fix race condition caused spinlock bad magic issue

[wangbiao]

From: wang, biao <biao.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Date: Mon, 11 Nov 2013 10:23:40 +0800
Subject: [PATCH] usbnet: fix race condition caused spinlock bad magic issue

there is race between usbnet_terminate_urbs and usbnet_bh.
for example:
    cpu 0                                     cpu 1
                                          usbnet_suspend
usbnet_bh {                               ->usbnet_terminate_urbs {
                                              dev->wait = &unlink_wakeup;
                                              while(....){..}//break
    if(dev->wait) is true
                       		              dev->wait=NULL
                                          }//unlink_wakeup is invalid
    __wake_up(dev->wait)//garbage value
}

the race is due to unprotection of dev->wait, so this patch involves a
spinlock to avoid it.

Signed-off-by: wang, biao <biao.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Signed-off-by: Zhang, Di <di.zhang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
 drivers/net/usb/usbnet.c |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 90a429b..f7df1af 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 spinlock_t dev_wait_lock = __SPIN_LOCK_UNLOCKED(dev_wait_lock);
 module_param (msg_level, int, 0);
 MODULE_PARM_DESC (msg_level, "Override default message level");
 
@@ -764,11 +765,14 @@ static void usbnet_terminate_urbs(struct usbnet *dev)
 	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(unlink_wakeup);
 	DECLARE_WAITQUEUE(wait, current);
 	int temp;
+	unsigned long flags;
 
 	/* ensure there are no more active urbs */
 	add_wait_queue(&unlink_wakeup, &wait);
 	set_current_state(TASK_UNINTERRUPTIBLE);
+	spin_lock_irqsave(&dev_wait_lock, flags);
 	dev->wait = &unlink_wakeup;
+	spin_unlock_irqrestore(&dev_wait_lock, flags);
 	temp = unlink_urbs(dev, &dev->txq) +
 		unlink_urbs(dev, &dev->rxq);
 
@@ -782,7 +786,9 @@ static void usbnet_terminate_urbs(struct usbnet *dev)
 				  "waited for %d urb completions\n", temp);
 	}
 	set_current_state(TASK_RUNNING);
+	spin_lock_irqsave(&dev_wait_lock, flags);
 	dev->wait = NULL;
+	spin_unlock_irqrestore(&dev_wait_lock, flags);
 	remove_wait_queue(&unlink_wakeup, &wait);
 }
 
@@ -1424,6 +1430,7 @@ static void usbnet_bh (unsigned long param)
 	struct usbnet		*dev = (struct usbnet *) param;
 	struct sk_buff		*skb;
 	struct skb_data		*entry;
+	unsigned long           flags;
 
 	while ((skb = skb_dequeue (&dev->done))) {
 		entry = (struct skb_data *) skb->cb;
@@ -1447,13 +1454,18 @@ static void usbnet_bh (unsigned long param)
 	clear_bit(EVENT_RX_KILL, &dev->flags);
 
 	// waiting for all pending urbs to complete?
+	spin_lock_irqsave(&dev_wait_lock, flags);
 	if (dev->wait) {
 		if ((dev->txq.qlen + dev->rxq.qlen + dev->done.qlen) == 0) {
-			wake_up (dev->wait);
+			wake_up(dev->wait);
 		}
+		spin_unlock_irqrestore(&dev_wait_lock, flags);
+		return;
+	}
+	spin_unlock_irqrestore(&dev_wait_lock, flags);
 
 	// or are we maybe short a few urbs?
-	} else if (netif_running (dev->net) &&
+	if (netif_running(dev->net) &&
 		   netif_device_present (dev->net) &&
 		   netif_carrier_ok(dev->net) &&
 		   !timer_pending (&dev->delay) &&
-- 
1.7.0.4



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Re: [PATCH V3] usbnet: fix race condition caused spinlock bad magic issue

[Oliver Neukum]

On Thu, 2013-11-14 at 10:03 +0800, wangbiao wrote:
> From: wang, biao <biao.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Date: Mon, 11 Nov 2013 10:23:40 +0800
> Subject: [PATCH] usbnet: fix race condition caused spinlock bad magic issue
> 
> there is race between usbnet_terminate_urbs and usbnet_bh.
> for example:
>     cpu 0                                     cpu 1
>                                           usbnet_suspend
> usbnet_bh {                               ->usbnet_terminate_urbs {
>                                               dev->wait = &unlink_wakeup;
>                                               while(....){..}//break
>     if(dev->wait) is true
>                        		              dev->wait=NULL
>                                           }//unlink_wakeup is invalid
>     __wake_up(dev->wait)//garbage value
> }
> 
> the race is due to unprotection of dev->wait, so this patch involves a
> spinlock to avoid it.
> 
> Signed-off-by: wang, biao <biao.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Zhang, Di <di.zhang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Acked-by: Oliver Neukum <oliver-GvhC2dPhHPQdnm+yROfE0A@public.gmane.org>

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Re: [PATCH V3] usbnet: fix race condition caused spinlock bad magic issue

[Ingo Molnar]

* wangbiao <biao.wang@intel.com> wrote:

> @@ -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 spinlock_t dev_wait_lock = __SPIN_LOCK_UNLOCKED(dev_wait_lock);
>  module_param (msg_level, int, 0);
>  MODULE_PARM_DESC (msg_level, "Override default message level");
>  

> @@ -1447,13 +1454,18 @@ static void usbnet_bh (unsigned long param)
>  	clear_bit(EVENT_RX_KILL, &dev->flags);
>  
>  	// waiting for all pending urbs to complete?

Please escape this code from the clutches of C++ style!

> +	spin_lock_irqsave(&dev_wait_lock, flags);
>  	if (dev->wait) {
>  		if ((dev->txq.qlen + dev->rxq.qlen + dev->done.qlen) == 0) {
> -			wake_up (dev->wait);
> +			wake_up(dev->wait);
>  		}
> +		spin_unlock_irqrestore(&dev_wait_lock, flags);
> +		return;
> +	}
> +	spin_unlock_irqrestore(&dev_wait_lock, flags);

The extra locking and the naked return from the middle of the 
control flow is a bit sad.

>  
>  	// or are we maybe short a few urbs?
> -	} else if (netif_running (dev->net) &&
> +	if (netif_running(dev->net) &&
>  		   netif_device_present (dev->net) &&
>  		   netif_carrier_ok(dev->net) &&
>  		   !timer_pending (&dev->delay) &&

While using a global spinlock from the probe/teardown methods is 
probably not a big deal, using it in usbnet_bh() looks rather 
unfortunate for performance and scalability of this driver.

I don't know the usbnet code at all, but is there really no 
natural per device synchronization method available for such 
cases? Could the race be avoided some other way? How do other 
drivers implement such kind of dev->wait handling?

Thanks,

	Ingo

Re: [PATCH V3] usbnet: fix race condition caused spinlock bad magic issue

[Bjørn Mork]

Oliver Neukum <oliver-GvhC2dPhHPQdnm+yROfE0A@public.gmane.org> writes:

> On Thu, 2013-11-14 at 10:03 +0800, wangbiao wrote:
>> From: wang, biao <biao.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>> Date: Mon, 11 Nov 2013 10:23:40 +0800
>> Subject: [PATCH] usbnet: fix race condition caused spinlock bad magic issue
>> 
>> there is race between usbnet_terminate_urbs and usbnet_bh.
>> for example:
>>     cpu 0                                     cpu 1
>>                                           usbnet_suspend
>> usbnet_bh {                               ->usbnet_terminate_urbs {
>>                                               dev->wait = &unlink_wakeup;
>>                                               while(....){..}//break
>>     if(dev->wait) is true
>>                        		              dev->wait=NULL
>>                                           }//unlink_wakeup is invalid
>>     __wake_up(dev->wait)//garbage value
>> }
>> 
>> the race is due to unprotection of dev->wait, so this patch involves a
>> spinlock to avoid it.
>> 
>> Signed-off-by: wang, biao <biao.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>> Signed-off-by: Zhang, Di <di.zhang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Acked-by: Oliver Neukum <oliver-GvhC2dPhHPQdnm+yROfE0A@public.gmane.org>


Really?  Serializing the suspend of all usbnet devices seems like a good
idea?


Bjørn
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