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 <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

include/net/phonet/pn_dev.h

···
 #define PN_DEV_H
 
 #include <linux/list.h>
-#include <linux/mutex.h>
 #include <linux/spinlock.h>
 
 struct net;

net/phonet/pn_dev.c

···
 #include <net/phonet/pn_dev.h>
 
 struct phonet_routes {
-	struct mutex		lock;
+	spinlock_t		lock;
 	struct net_device __rcu	*table[64];
 };
 
···
 
 	/* 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 */
···
 
 	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;
 }
 
···
 	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;
 }
 
···
 	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;