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[PATCH] lockd: fix races in per-net NSM client handling [message #48590] Wed, 24 October 2012 10:18
Stanislav Kinsbursky is currently offline  Stanislav Kinsbursky
Messages: 683
Registered: October 2011
Senior Member
From: *parallels.com
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@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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