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

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Message-ID: <4BB409A1.7090701@redhat.com>
Date:	Thu, 01 Apr 2010 10:49:05 +0800
From:	Cong Wang <amwang@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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()

Eric W. Biederman wrote:
> 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.


This is reasonable, because workqueue flush functions will potentially
call all the work functions which could take the same lock taken before
the flush call, thus deadlock.

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

It's only a lockdep warning.

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

Oh, this seems a better idea, as long as the destructor are not called
with any locks holding.

Thanks!
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