linux-kernel - [PATCH] lockd: fix races in per-net NSM client handling

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Date:	Wed, 24 Oct 2012 14:18:10 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	Trond.Myklebust@...app.com
Cc:	bfields@...ldses.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, devel@...nvz.org
Subject: [PATCH] lockd: fix races in per-net NSM client handling

This patch fixes two problems:
1) Removes races on NSM creation.
2) Fixes silly misprint on NSM client destruction (usage counter was checked
for non-zero value instead of zero).

Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
---
 fs/lockd/mon.c |   35 +++++++++++++++++++++++------------
 1 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/fs/lockd/mon.c b/fs/lockd/mon.c
index e4fb3ba..e3e59f6 100644
--- a/fs/lockd/mon.c
+++ b/fs/lockd/mon.c
@@ -85,30 +85,41 @@ static struct rpc_clnt *nsm_create(struct net *net)
 	return rpc_create(&args);
 }
 
-static struct rpc_clnt *nsm_client_get(struct net *net)
+static struct rpc_clnt *nsm_get_client(struct net *net)
 {
-	static DEFINE_MUTEX(nsm_create_mutex);
-	struct rpc_clnt	*clnt;
+	struct rpc_clnt *clnt = NULL;
 	struct lockd_net *ln = net_generic(net, lockd_net_id);
 
 	spin_lock(&ln->nsm_clnt_lock);
 	if (ln->nsm_users) {
 		ln->nsm_users++;
 		clnt = ln->nsm_clnt;
-		spin_unlock(&ln->nsm_clnt_lock);
-		goto out;
 	}
 	spin_unlock(&ln->nsm_clnt_lock);
+	return clnt;
+}
+
+static struct rpc_clnt *nsm_client_get(struct net *net)
+{
+	static DEFINE_MUTEX(nsm_create_mutex);
+	struct rpc_clnt	*clnt;
+	struct lockd_net *ln = net_generic(net, lockd_net_id);
+
+	clnt = nsm_get_client(net);
+	if (clnt)
+		return clnt;
 
 	mutex_lock(&nsm_create_mutex);
-	clnt = nsm_create(net);
-	if (!IS_ERR(clnt)) {
-		ln->nsm_clnt = clnt;
-		smp_wmb();
-		ln->nsm_users = 1;
+	clnt = nsm_get_client(net);
+	if (clnt == NULL) {
+		clnt = nsm_create(net);
+		if (!IS_ERR(clnt)) {
+			ln->nsm_clnt = clnt;
+			smp_wmb();
+			ln->nsm_users = 1;
+		}
 	}
 	mutex_unlock(&nsm_create_mutex);
-out:
 	return clnt;
 }
 
@@ -120,7 +131,7 @@ static void nsm_client_put(struct net *net)
 
 	spin_lock(&ln->nsm_clnt_lock);
 	if (ln->nsm_users) {
-		if (--ln->nsm_users)
+		if (--ln->nsm_users == 0)
 			ln->nsm_clnt = NULL;
 		shutdown = !ln->nsm_users;
 	}

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