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

[Paolo Bonzini]

Il 03/06/2014 15:57, Eric Dumazet ha scritto:
> On Tue, 2014-06-03 at 14:48 +0200, 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.
>
> Look at how we did this in commit
> c3059477fce2d956a0bb3e04357324780c5d8eeb

That would make VHOST_SET_MEMORY as slow as before (even though once 
every few times).

> > > 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.
>
> Yep, this is what I pointed out. This is not only necessary, but
> confusing and might be incorrectly copy/pasted in the future.
>
> This patch is a partial one and leaves confusion.

I agree.

Paolo
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