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

[Stanislav Kinsbursky]

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 <skinsbur...@parallels.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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