linux-kernel - Re: [PATCH] NFS: Fix RCU warnings in nfs_inode_return_delegation

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Message-ID: <15371.1270057054@redhat.com>
Date:	Wed, 31 Mar 2010 18:37:34 +0100
From:	David Howells <dhowells@...hat.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	dhowells@...hat.com, Eric Dumazet <eric.dumazet@...il.com>,
	Trond.Myklebust@...app.com, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NFS: Fix RCU warnings in nfs_inode_return_delegation_noreclaim() [ver #2]

Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> Protected by something that the caller did, be it holding the the correct
> lock, operating on it during initialization before other CPUs have access
> to it, operating on it during cleanup after other CPUs' access has been
> revoked, or whatever.

But the point I made very early this morning still stands:  What if someone
simply wants to test the pointer, not actually to dereference it?

NFS was using rcu_dereference() for this in a couple of places - which is
overkill.  I suggested stripping this off and you countered with the
suggestion that it should be using rcu_dereference_check().

Why do I need anything at all?

David
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