netdev - Re: [RFC PATCH v1] tun: Cleanup error handling in tun_set

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Date:	Thu, 06 Aug 2009 03:21:41 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Paul Moore <paul.moore@...com>, netdev@...r.kernel.org,
	David Miller <davem@...emloft.net>
Subject: Re: [RFC PATCH v1] tun: Cleanup error handling in tun_set_iff()

Herbert Xu <herbert@...dor.apana.org.au> writes:

> On Wed, Aug 05, 2009 at 05:38:42PM -0400, Paul Moore wrote:
>>
>> My concern is that I believe that if the kernel fails at an operation it 
>> should do all it can to unwind any actions it took in the course of attempting 
>> to perform the requested operation.  Leaving a TUN device around in the case 
>> of a tun_attach() failure seems like the kernel is being lazy, sure a user can 
>> cleanup the device but why should they have to?
>
> That particular tun_attach should never fail.  Perhaps you can
> just add a WARN_ON.

Two threads one file descriptor.  Both simultaneously attempt to 
attach to a tun device.  One will fail, the other succeed.

At least that is how I read the locking.

Eric
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