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Date:	Wed, 23 Jul 2014 11:11:14 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Li RongQing <roy.qing.li@...il.com>
cc:	netdev <netdev@...r.kernel.org>, linux-usb@...r.kernel.org,
	jeff.westfahl@...com
Subject: Re: [BUG] Lockdep splat in usb network gadget

On Wed, 23 Jul 2014, Li RongQing wrote:

> This commit introduced this bug
> 
> commit a9232076374334ca2bc2a448dfde96d38a54349a
> Author: Jeff Westfahl <jeff.westfahl@...com>
> Date:   Thu May 29 09:49:41 2014 +0300
> 
>     usb: gadget: u_ether: synchronize with transmit when stopping queue
> 
>     When disconnecting, it's possible that another thread has already made it
>     into eth_start_xmit before we call netif_stop_queue. This can lead to a
>     crash as eth_start_xmit tries to use resources that gether_disconnect is
>     freeing. Use netif_tx_lock/unlock around netif_stop_queue to ensure no
>     threads are executing during the remainder of gether_disconnect.
> 
>     Signed-off-by: Jeff Westfahl <jeff.westfahl@...com>
>     Tested-by: Jaeden Amero <jaeden.amero@...com>
>     Signed-off-by: Felipe Balbi <balbi@...com>

So what's the fix?
 
> diff --git a/drivers/usb/gadget/u_ether.c b/drivers/usb/gadget/u_ether.c
> index 3d78a88..97b0277 100644
> --- a/drivers/usb/gadget/u_ether.c
> +++ b/drivers/usb/gadget/u_ether.c
> @@ -1120,7 +1120,10 @@ void gether_disconnect(struct gether *link)
> 
>         DBG(dev, "%s\n", __func__);
> 
> +       netif_tx_lock(dev->net);
>         netif_stop_queue(dev->net);
> +       netif_tx_unlock(dev->net);
> +
>         netif_carrier_off(dev->net);
--
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