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Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections

To: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Subject: Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections
From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Date: Thu, 29 Sep 2005 08:11:10 +1000
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>, suzannew@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Robert.Olsson@xxxxxxxxxxx, walpole@xxxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <20050928145110.GA4925@xxxxxxxxxx>
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On Wed, Sep 28, 2005 at 07:51:10AM -0700, Paul E. McKenney wrote:
> The reference-count approach is only guaranteed to work if the kernel
> thread that did the reference-count increment is later referencing that
> same data element.  Otherwise, one has the following possible situation
> on DEC Alpha:

You're quite right.  Without the rcu_dereference users of in_dev_get()
may see pre-initialisation contents of in_dev.

So these barriers are definitely needed.

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