netdev - Re: [PULL 2/2] vhost: replace rcu with mutex

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Message-ID: <538DCF15.4080904@gmail.com>
Date:	Tue, 03 Jun 2014 09:35:17 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
CC:	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	David Miller <davem@...emloft.net>
Subject: Re: [PULL 2/2] vhost: replace rcu with mutex

On 06/03/2014 08:48 AM, Paolo Bonzini wrote:
> Il 02/06/2014 23:58, Eric Dumazet ha scritto:
>> This looks dubious
>>
>> What about using kfree_rcu() instead ?
> 
> It would lead to unbound allocation from userspace.
> 
>> translate_desc() still uses rcu_read_lock(), its not clear if the mutex
>> is really held.
> 
> Yes, vhost_get_vq_desc must be called with the vq mutex held.
> 
> The rcu_read_lock/unlock in translate_desc is unnecessary.
> 

If that's true, then does dev->memory really needs to be rcu protected?
It appears to always be read under mutex.

-vlad

> Paolo
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