netdev - Re: [Patch] bonding: fix potential deadlock in bond

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Date:	Wed, 31 Mar 2010 04:28:33 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Amerigo Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Jiri Pirko <jpirko@...hat.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	bonding-devel@...ts.sourceforge.net,
	Jay Vosburgh <fubar@...ibm.com>
Subject: Re: [Patch] bonding: fix potential deadlock in bond_uninit()

Amerigo Wang <amwang@...hat.com> writes:

> bond_uninit() is invoked with rtnl_lock held, when it does destroy_workqueue()
> which will potentially flush all works in this workqueue, if we hold rtnl_lock
> again in the work function, it will deadlock.
>
> So unlock rtnl_lock before calling destroy_workqueue().

Ouch.  That seems rather rude to our caller, and likely very
dangerous.

Is this a deadlock you actually hit, or is this something lockdep
warned about?

My gut feel says we need to move the destroy_workqueue into
the network device destructor.

Eric



> Signed-off-by: WANG Cong <amwang@...hat.com>
> Cc: Jay Vosburgh <fubar@...ibm.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Stephen Hemminger <shemminger@...tta.com>
> Cc: Jiri Pirko <jpirko@...hat.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
>
> ---
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 5b92fbf..b781728 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -4542,8 +4542,11 @@ static void bond_uninit(struct net_device *bond_dev)
>  
>  	bond_remove_proc_entry(bond);
>  
> -	if (bond->wq)
> +	if (bond->wq) {
> +		rtnl_unlock();
>  		destroy_workqueue(bond->wq);
> +		rtnl_lock();
> +	}
>  
>  	netif_addr_lock_bh(bond_dev);
>  	bond_mc_list_destroy(bond);
--
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