From 28ed3ab34ffabbcd3957ff85d5941b39c50b05db Mon Sep 17 00:00:00 2001
From: Chris Lew <clew@codeaurora.org>
Date: Tue, 19 May 2020 18:54:43 -0700
Subject: [PATCH] net: qrtr: Remove rcu logic for port lookup/remove

synchronize_rcu() is slow and can create delays on creating/removing
sockets.

Some clients have latency requirements for spinning off a
thread that creates a client and lookup sockets for some sessions. They
close the lookup socket during this sequence which causes delays. Each
call to synchronize_rcu takes 20-40 ms which is too long.

Remove the rcu logic and change qrtr_port_lock to a spinlock so it can
be used in qrtr_port_lookup which may be used in atomic context.

Change-Id: I3244e31d3ca0599df794d3936033735bcdd3e972
Signed-off-by: Chris Lew <clew@codeaurora.org>
---
 net/qrtr/qrtr.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
index 57469f4898b9..1753201d4ac4 100644
--- a/net/qrtr/qrtr.c
+++ b/net/qrtr/qrtr.c
@@ -128,7 +128,7 @@ static DECLARE_RWSEM(qrtr_epts_lock);
 
 /* local port allocation management */
 static DEFINE_IDR(qrtr_ports);
-static DEFINE_MUTEX(qrtr_port_lock);
+static DEFINE_SPINLOCK(qrtr_port_lock);
 
 /**
  * struct qrtr_node - endpoint node
@@ -1191,15 +1191,16 @@ EXPORT_SYMBOL_GPL(qrtr_endpoint_unregister);
 static struct qrtr_sock *qrtr_port_lookup(int port)
 {
 	struct qrtr_sock *ipc;
+	unsigned long flags;
 
 	if (port == QRTR_PORT_CTRL)
 		port = 0;
 
-	rcu_read_lock();
+	spin_lock_irqsave(&qrtr_port_lock, flags);
 	ipc = idr_find(&qrtr_ports, port);
 	if (ipc)
 		sock_hold(&ipc->sk);
-	rcu_read_unlock();
+	spin_unlock_irqrestore(&qrtr_port_lock, flags);
 
 	return ipc;
 }
@@ -1261,6 +1262,7 @@ exit:
 static void qrtr_port_remove(struct qrtr_sock *ipc)
 {
 	int port = ipc->us.sq_port;
+	unsigned long flags;
 
 	qrtr_send_del_client(ipc);
 	if (port == QRTR_PORT_CTRL)
@@ -1268,13 +1270,9 @@ static void qrtr_port_remove(struct qrtr_sock *ipc)
 
 	__sock_put(&ipc->sk);
 
-	mutex_lock(&qrtr_port_lock);
+	spin_lock_irqsave(&qrtr_port_lock, flags);
 	idr_remove(&qrtr_ports, port);
-	mutex_unlock(&qrtr_port_lock);
-
-	/* Ensure that if qrtr_port_lookup() did enter the RCU read section we
-	 * wait for it to up increment the refcount */
-	synchronize_rcu();
+	spin_unlock_irqrestore(&qrtr_port_lock, flags);
 }
 
 /* Assign port number to socket.
@@ -1348,6 +1346,7 @@ static int __qrtr_bind(struct socket *sock,
 {
 	struct qrtr_sock *ipc = qrtr_sk(sock->sk);
 	struct sock *sk = sock->sk;
+	unsigned long flags;
 	int port;
 	int rc;
 
@@ -1355,17 +1354,18 @@ static int __qrtr_bind(struct socket *sock,
 	if (!zapped && addr->sq_port == ipc->us.sq_port)
 		return 0;
 
-	mutex_lock(&qrtr_port_lock);
+	spin_lock_irqsave(&qrtr_port_lock, flags);
 	port = addr->sq_port;
 	rc = qrtr_port_assign(ipc, &port);
 	if (rc) {
-		mutex_unlock(&qrtr_port_lock);
+		spin_unlock_irqrestore(&qrtr_port_lock, flags);
 		return rc;
 	}
 	/* Notify all open ports about the new controller */
 	if (port == QRTR_PORT_CTRL)
 		qrtr_reset_ports();
-	mutex_unlock(&qrtr_port_lock);
+	spin_unlock_irqrestore(&qrtr_port_lock, flags);
+
 
 	if (port == QRTR_PORT_CTRL) {
 		struct qrtr_node *node;