netdev - RE: [PATCH v2 1/4] SUNRPC: release per-net clients lock before calling PipeFS dentries creation

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Date:	Mon, 27 Feb 2012 17:11:37 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Stanislav Kinsbursky" <skinsbursky@...allels.com>,
	"Myklebust, Trond" <Trond.Myklebust@...app.com>
Cc:	<linux-nfs@...r.kernel.org>,
	"Pavel Emelianov" <xemul@...allels.com>, <neilb@...e.de>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	"James Bottomley" <jbottomley@...allels.com>,
	<bfields@...ldses.org>, <davem@...emloft.net>, <devel@...nvz.org>
Subject: RE: [PATCH v2 1/4] SUNRPC: release per-net clients lock before calling PipeFS dentries creation

 
> Gmmm.
> Please, correct me, if I'm wrong, that you are proposing 
> something like this:
> 
>    	spin_lock(&sn->rpc_client_lock);
> again:
> 	list_for_each_entry(clnt,&sn->all_clients, cl_clients) {
> 		if ((event == RPC_PIPEFS_MOUNT) && clnt->cl_dentry) ||
> 		    (event == RPC_PIPEFS_UMOUNT) && !clnt->cl_dentry))
> 			continue;
> 		atomic_inc(&clnt->cl_count);
> 		spin_unlock(&sn->rpc_client_lock);
>     		error = __rpc_pipefs_event(clnt, event, sb);
> 		rpc_release_client(clnt);
> 		spin_lock(&sn->rpc_client_lock);
>     		if (error)
>     			break;
> 		goto again;
>     	}
>     	spin_unlock(&sn->rpc_client_lock);

You might manage to request reference to the 'next'
item while holding the lock. So maybe a loop that has:

	error = ...
	if (error) {
		rpc_release_client(clnt);
		break;
	}
	spin_lock(&sn->rpc_client_lock);
	next_clnt = list_next(clnt);
	if (next_clnt)
		atomic_inc(&next_clnt->cl_count);
	spin_unlock(&sn->rpc_client_lock);
	rpc_release_client(clnt);
	clnt = next_clnt;
   } while (clnt != NULL);

	David


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