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

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Message-ID: <19197.1268761204@redhat.com>
Date:	Tue, 16 Mar 2010 17:40:04 +0000
From:	David Howells <dhowells@...hat.com>
To:	Trond Myklebust <Trond.Myklebust@...app.com>
Cc:	dhowells@...hat.com, paulmck@...ux.vnet.ibm.com,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NFS: Fix RCU warnings in nfs_inode_return_delegation_noreclaim()

Trond Myklebust <Trond.Myklebust@...app.com> wrote:

> > The lock is probably held here, in which case something like the
> > following would work well without needing the artificial rcu_read_lock()
> > and rcu_read_unlock():
> 
> No. The lock is not held here. At this point, the delegation has been
> detached from the inode that pointed to it, and so we can free up its
> contents.
> 
> We still need the call_rcu() to free up the allocated memory in order to
> ensure that some process doing lockless traversal of the
> clp->cl_delegations list doesn't crash.

In that case, surely you can't detach the credentials pointer until the
callback is invoked?

David
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