netdev - Re: [PATCH] net: deadlock during net device unregistration

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Message-Id: <20081007.155039.199136099.davem@davemloft.net>
Date:	Tue, 07 Oct 2008 15:50:39 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	benjamin.thery@...l.net, netdev@...r.kernel.org,
	dlezcano@...ibm.com
Subject: Re: [PATCH] net: deadlock during net device unregistration

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Sun, 05 Oct 2008 12:26:21 +0800

> net: Fix netdev_run_todo dead-lock
> 
> Benjamin Thery tracked down a bug that explains many instances
> of the error
> 
> unregister_netdevice: waiting for %s to become free. Usage count = %d
> 
> It turns out that netdev_run_todo can dead-lock with itself if
> a second instance of it is run in a thread that will then free
> a reference to the device waited on by the first instance.
> 
> The problem is really quite silly.  We were trying to create
> parallelism where none was required.  As netdev_run_todo always
> follows a RTNL section, and that todo tasks can only be added
> with the RTNL held, by definition you should only need to wait
> for the very ones that you've added and be done with it.
> 
> There is no need for a second mutex or spinlock.
> 
> This is exactly what the following patch does.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

Ok, this looks safe.  I've applied this to net-2.6, thanks!
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