netdev - Re: [Lguest] [PATCH 4/5] lguest: use KVM hypercalls

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Date:	Wed, 15 Apr 2009 21:28:02 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Patrick McHardy <kaber@...sh.net>,
	Matias Zabaljauregui <zabaljauregui@...il.com>, odie@...aau.dk,
	Rusty Russell <rusty@...tcorp.com.au>, lguest@...abs.org,
	virtualization@...ts.osdl.org,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [Lguest] [PATCH 4/5] lguest: use KVM hypercalls

On Wed, Apr 15, 2009 at 06:23:29AM -0700, Eric W. Biederman wrote:
> 
> There is a GIGANTIC reason to have the wait queue on tfile.
> 
> If you open a file, and do ip link del tapN you can still
> be blocked waiting in poll.
> 
> The problem is specifically free_poll_entry, where we call
> remove_wait_queue and fput without calling any file methods.
> So all of this happens without struct tun_file's count being
> elevated.  Which means tun_net_uninit can detach before we get
> off of the stupid poll wait queue.

What about taking a netdev refcount before calling poll_wait?

Thanks,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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