linux-kernel - Re: [PATCH 2/4] NFS: replace per-net client lock by mutex

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Date:	Mon, 27 Feb 2012 15:00:18 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
CC:	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"xemul@...allels.com" <xemul@...allels.com>,
	"neilb@...e.de" <neilb@...e.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jbottomley@...allels.com" <jbottomley@...allels.com>,
	"bfields@...ldses.org" <bfields@...ldses.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [PATCH 2/4] NFS: replace per-net client lock by mutex

On Mon, 2012-02-27 at 17:49 +0400, Stanislav Kinsbursky wrote:
> Lockdep is sad otherwise, because inode mutex is taken on PipeFS dentry
> creation, which can be called on mount notification, where this per-net client
> lock is taken on clients list walk.
> 
> Note: I used simple mutex instead of rw semaphore because of
> nfs_put_client->atomic_dec_and_mutex_lock() call. Probably, there is a better
> solution here.
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
> 

This is overkill... We end up blocking NFSv4 callbacks while the
rpc_pipefs notifier runs through the nfs_clients creating or destroying
idmapper dentries.

Surely the rpc_pipefs_event() can take a reference to the nfs_client and
then drop the spin_lock if it sees that it needs to create or destroy a
dentry?

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com