From 3deec3b4afb4c767007eae1eeedbcf3da599395b Mon Sep 17 00:00:00 2001
From: Kuniyuki Iwashima <kuniyu@amazon.com>
Date: Thu, 17 Oct 2024 11:31:39 -0700
Subject: [PATCH] phonet: Convert phonet_routes.lock to spinlock_t.

route_doit() calls phonet_route_add() or phonet_route_del()
for RTM_NEWROUTE or RTM_DELROUTE, respectively.

Both functions only touch phonet_pernet(dev_net(dev))->routes,
which is currently protected by RTNL and its dedicated mutex,
phonet_routes.lock.

We will convert route_doit() to RCU and cannot use mutex inside RCU.

Let's convert the mutex to spinlock_t.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/net/phonet/pn_dev.h |  1 -
 net/phonet/pn_dev.c         | 23 ++++++++++++++---------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/include/net/phonet/pn_dev.h b/include/net/phonet/pn_dev.h
index 021e524fd20a..37a3e83531c6 100644
--- a/include/net/phonet/pn_dev.h
+++ b/include/net/phonet/pn_dev.h
@@ -11,7 +11,6 @@
 #define PN_DEV_H
 
 #include <linux/list.h>
-#include <linux/mutex.h>
 #include <linux/spinlock.h>
 
 struct net;
diff --git a/net/phonet/pn_dev.c b/net/phonet/pn_dev.c
index 6ded0d347b9f..19234d664c4f 100644
--- a/net/phonet/pn_dev.c
+++ b/net/phonet/pn_dev.c
@@ -22,7 +22,7 @@
 #include <net/phonet/pn_dev.h>
 
 struct phonet_routes {
-	struct mutex		lock;
+	spinlock_t		lock;
 	struct net_device __rcu	*table[64];
 };
 
@@ -273,13 +273,15 @@ static void phonet_route_autodel(struct net_device *dev)
 
 	/* Remove left-over Phonet routes */
 	bitmap_zero(deleted, 64);
-	mutex_lock(&pnn->routes.lock);
-	for (i = 0; i < 64; i++)
+
+	spin_lock(&pnn->routes.lock);
+	for (i = 0; i < 64; i++) {
 		if (rcu_access_pointer(pnn->routes.table[i]) == dev) {
 			RCU_INIT_POINTER(pnn->routes.table[i], NULL);
 			set_bit(i, deleted);
 		}
-	mutex_unlock(&pnn->routes.lock);
+	}
+	spin_unlock(&pnn->routes.lock);
 
 	if (bitmap_empty(deleted, 64))
 		return; /* short-circuit RCU */
@@ -326,7 +328,7 @@ static int __net_init phonet_init_net(struct net *net)
 
 	INIT_LIST_HEAD(&pnn->pndevs.list);
 	spin_lock_init(&pnn->pndevs.lock);
-	mutex_init(&pnn->routes.lock);
+	spin_lock_init(&pnn->routes.lock);
 	return 0;
 }
 
@@ -376,13 +378,15 @@ int phonet_route_add(struct net_device *dev, u8 daddr)
 	int err = -EEXIST;
 
 	daddr = daddr >> 2;
-	mutex_lock(&routes->lock);
+
+	spin_lock(&routes->lock);
 	if (routes->table[daddr] == NULL) {
 		rcu_assign_pointer(routes->table[daddr], dev);
 		dev_hold(dev);
 		err = 0;
 	}
-	mutex_unlock(&routes->lock);
+	spin_unlock(&routes->lock);
+
 	return err;
 }
 
@@ -392,12 +396,13 @@ int phonet_route_del(struct net_device *dev, u8 daddr)
 	struct phonet_routes *routes = &pnn->routes;
 
 	daddr = daddr >> 2;
-	mutex_lock(&routes->lock);
+
+	spin_lock(&routes->lock);
 	if (rcu_access_pointer(routes->table[daddr]) == dev)
 		RCU_INIT_POINTER(routes->table[daddr], NULL);
 	else
 		dev = NULL;
-	mutex_unlock(&routes->lock);
+	spin_unlock(&routes->lock);
 
 	if (!dev)
 		return -ENOENT;