linux-kernel - [PATCH] NFS: init client before declaration

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Date:	Tue, 22 May 2012 16:40:49 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	Trond.Myklebust@...app.com
Cc:	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	devel@...nvz.org
Subject: [PATCH] NFS: init client before declaration

Client have to be initialized prior to adding it to per-net clients list,
because otherwise there are races, shown below:

CPU#0					CPU#1
_____					_____

nfs_get_client
nfs_alloc_client
list_add(..., nfs_client_list)
					rpc_fill_super
					rpc_pipefs_event
					nfs_get_client_for_event
					__rpc_pipefs_event
					(clp->cl_rpcclient is uninitialized)
					BUG()
init_client
clp->cl_rpcclient = ...


Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
---
 fs/nfs/client.c |   22 ++++++++++++----------
 1 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index ae29d4f..9bf4702 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -525,7 +525,7 @@ nfs_get_client(const struct nfs_client_initdata *cl_init,
 		cl_init->hostname ?: "", cl_init->rpc_ops->version);
 
 	/* see if the client already exists */
-	do {
+	while (1) {
 		spin_lock(&nn->nfs_client_lock);
 
 		clp = nfs_match_client(cl_init);
@@ -537,10 +537,18 @@ nfs_get_client(const struct nfs_client_initdata *cl_init,
 		spin_unlock(&nn->nfs_client_lock);
 
 		new = nfs_alloc_client(cl_init);
-	} while (!IS_ERR(new));
+		if (IS_ERR(new)) {
+			dprintk("--> nfs_get_client() = %ld [failed]\n", PTR_ERR(new));
+			return new;
+		}
 
-	dprintk("--> nfs_get_client() = %ld [failed]\n", PTR_ERR(new));
-	return new;
+		error = cl_init->rpc_ops->init_client(new, timeparms, ip_addr,
+						      authflavour, noresvport);
+		if (error < 0) {
+			nfs_put_client(new);
+			return ERR_PTR(error);
+		}
+	}
 
 	/* install a new client and return with it unready */
 install_client:
@@ -548,12 +556,6 @@ install_client:
 	list_add(&clp->cl_share_link, &nn->nfs_client_list);
 	spin_unlock(&nn->nfs_client_lock);
 
-	error = cl_init->rpc_ops->init_client(clp, timeparms, ip_addr,
-					      authflavour, noresvport);
-	if (error < 0) {
-		nfs_put_client(clp);
-		return ERR_PTR(error);
-	}
 	dprintk("--> nfs_get_client() = %p [new]\n", clp);
 	return clp;
 

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