netdev - Re: [PATCH net-next 2/2] sunvnet: vnet_start

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Date:	Wed, 01 Oct 2014 12:05:24 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:	davem@...emloft.net, raghuram.kothakota@...cle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] sunvnet: vnet_start_xmit() must hold a
 refcnt on port.

On Wed, 2014-10-01 at 14:56 -0400, Sowmini Varadhan wrote:
> A vnet_port_remove could be triggered as a result of an ldm-unbind operation
> by the peer, or a module unload, or other changes to the inter-vnet-link
> configuration.  When this is concurrent with vnet_start_xmit(),
> the following sequence could occur
> 
>   thread 1                                    thread 2
> vnet_start_xmit
>  -> tx_port_find
>     spin_lock_irqsave(&vp->lock..)
>     ret = __tx_port_find(..)
>     spin_lock_irqrestore(&vp->lock..)
>                                            vio_remove -> ..
>                                                ->vnet_port_remove
>                                            spin_lock_irqsave(&vp->lock..)
>                                            cleanup
>                                            spin_lock_irqrestore(&vp->lock..)
>                                            kfree(port)
>  /* attempt to use ret will bomb */
> 
> This patch avoids the problem by holding/releasing a refcnt on
> the vnet_port.

Hmpff... This calls for rcu protection here !


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