linux-kernel - Re: [PATCH RFC] hlist_add_tail

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Date:   Mon, 5 Dec 2016 05:29:23 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     paulmck@...ux.vnet.ibm.com, arnd@...db.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] hlist_add_tail_rcu disable sparse warning

On Fri, Nov 25, 2016 at 07:52:23PM -0500, David Miller wrote:
> From: "Michael S. Tsirkin" <mst@...hat.com>
> Date: Wed, 23 Nov 2016 22:48:19 +0200
> 
> > I would appreciate review to confirm the function doesn't
> > do anything unsafe though.
> > 
> > In particular, should this use __hlist_for_each_rcu instead?
> > I note that __hlist_for_each_rcu does rcu_dereference
> > internally, which is missing here.
> 
> I personally think it should use __hlist_for_each_rcu, otherwise
> nothing expresses the rcu-ness of the operation.

What does "rcu-ness" mean in this context?

The question is not just about making the code pretty.

This operation is called outside any rcu critical section.
If you are going to call __hlist_for_each_rcu which
calls rcu_dereference, you should do it inside
a critical section.

Other operations such as hlist_add_behind_rcu manipulate
lists manually, maybe this one should, too?
Paul?

-- 
MST