Re: [PATCH v5 1/8] SUNRPC: introduce helpers for reference counted rpcbind clients

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20.09.2011 18:24, Jeff Layton пишет:
On Tue, 20 Sep 2011 17:49:27 +0400
Stanislav Kinsbursky<skinsbursky@xxxxxxxxxxxxx>  wrote:

v5: fixed races with rpcb_users in rpcb_get_local()

This helpers will be used for dynamical creation and destruction of rpcbind
clients.
Variable rpcb_users is actually a counter of lauched RPC services. If rpcbind
clients has been created already, then we just increase rpcb_users.

Signed-off-by: Stanislav Kinsbursky<skinsbursky@xxxxxxxxxxxxx>

---
   net/sunrpc/rpcb_clnt.c |   53 ++++++++++++++++++++++++++++++++++++++++++++++++
   1 files changed, 53 insertions(+), 0 deletions(-)

diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c
index e45d2fb..5f4a406 100644
--- a/net/sunrpc/rpcb_clnt.c
+++ b/net/sunrpc/rpcb_clnt.c
@@ -114,6 +114,9 @@ static struct rpc_program	rpcb_program;
   static struct rpc_clnt *	rpcb_local_clnt;
   static struct rpc_clnt *	rpcb_local_clnt4;
   +DEFINE_SPINLOCK(rpcb_clnt_lock);
+unsigned int			rpcb_users;
+
   struct rpcbind_args {
   	struct rpc_xprt *	r_xprt;
   @@ -161,6 +164,56 @@ static void rpcb_map_release(void *data)
   	kfree(map);
   }
   +static int rpcb_get_local(void)
+{
+	int cnt;
+
+	spin_lock(&rpcb_clnt_lock);
+	if (rpcb_users)
+		rpcb_users++;
+	cnt = rpcb_users;
+	spin_unlock(&rpcb_clnt_lock);
+
+	return cnt;
+}
+
+void rpcb_put_local(void)
+{
+	struct rpc_clnt *clnt = rpcb_local_clnt;
+	struct rpc_clnt *clnt4 = rpcb_local_clnt4;
+	int shutdown;
+
+	spin_lock(&rpcb_clnt_lock);
+	if (--rpcb_users == 0) {
+		rpcb_local_clnt = NULL;
+		rpcb_local_clnt4 = NULL;
+	}

In the function below, you mention that the above pointers are
protected by rpcb_create_local_mutex, but it looks like they get reset
here without that being held?


Assigning of them is protected by rpcb_create_local_mutex.
Dereferencing of them is protected by rpcb_clnt_lock.

Might it be simpler to just protect rpcb_users with the
rpcb_create_local_mutex and ensure that it's held whenever you call one
of these routines? None of these are codepaths are particularly hot.


I just inherited this lock-mutex logic.
Actually, you right. This codepaths are used rarely.
But are use sure, that we need to remove this "speed-up" logic if we take into account that it was here already?

+	shutdown = !rpcb_users;
+	spin_unlock(&rpcb_clnt_lock);
+
+	if (shutdown) {
+		/*
+		 * cleanup_rpcb_clnt - remove xprtsock's sysctls, unregister
+		 */
+		if (clnt4)
+			rpc_shutdown_client(clnt4);
+		if (clnt)
+			rpc_shutdown_client(clnt);
+	}
+	return;
+}
+
+static void rpcb_set_local(struct rpc_clnt *clnt, struct rpc_clnt *clnt4)
+{
+	/* Protected by rpcb_create_local_mutex */
+	rpcb_local_clnt = clnt;
+	rpcb_local_clnt4 = clnt4;
+	rpcb_users++;
+	dprintk("RPC:       created new rpcb local clients (rpcb_local_clnt: "
+			"%p, rpcb_local_clnt4: %p)\n", rpcb_local_clnt,
+			rpcb_local_clnt4);
+}
+
   /*
    * Returns zero on success, otherwise a negative errno value
    * is returned.
--
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--
Best regards,
Stanislav Kinsbursky
--
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