Remove ethernet interface logic for SoftAP and STA

Issue: The problem is that there is a race condition introduced in that the LWIP thread is relying on the
interface as it is taken down by a application thread while calling disconnect.
In disconnect api called from application context, whd_emac_wifi_link_state_changed() will refer to netif interface
structure in its callback api netif_link_irq(netif). This netif will be cleared by remove_etherent_interface().
whd_emac_wifi_link_state_changed will post message to tcpip_thread. tcpip_thread will process the message and
call the callback api netif_link_irq(netif)
Calling sequence is whd_emac_wifi_link_state_changed -> remove_etherent_interface(). Hence there is a timing issue
that netif might be cleared first before tcpip thread process the message netif_link_irq(netif)

Fix: remove_etherent_interface() will post message to tcpip thread and tcpip:
thread process the message delete_interface()
which will actually remove the inferface from the netif_list.
Calling sequence is whd_emac_wifi_link_state_changed() message post -> remove_etherent_interface() message post.
message processing order netif_link_irq(netif) -> delete_interface().
Since both the processing is handled in single thread, processing of message is handled sequentially.

Author: Arun S

features/lwipstack/LWIPInterface.cpp

@@ -494,6 +494,11 @@ LWIP::Interface::Interface() :
     attr.cb_mem = &has_any_addr_sem;
     attr.cb_size = sizeof has_any_addr_sem;
     has_any_addr = osSemaphoreNew(UINT16_MAX, 0, &attr);
+
+    attr.cb_mem = &remove_interface_sem;
+    attr.cb_size = sizeof remove_interface_sem;
+    remove_interface = osSemaphoreNew(UINT16_MAX, 0, &attr);
+
 #if PREF_ADDR_TIMEOUT
     attr.cb_mem = &has_pref_addr_sem;
     attr.cb_size = sizeof has_pref_addr_sem;
@@ -565,6 +570,49 @@ nsapi_error_t LWIP::add_ethernet_interface(EMAC &emac, bool default_if, OnboardN
 #endif //LWIP_ETHERNET
 }
 
+void LWIP::Interface::delete_interface(OnboardNetworkStack::Interface **interface_out)
+{
+#if LWIP_ETHERNET
+    if ((interface_out != NULL) && (*interface_out != NULL)) {
+        LWIP::Interface *lwip = static_cast<Interface *>(*interface_out);
+        LWIP::Interface *node = lwip->list;
+
+        if (lwip->list != NULL) {
+            if (lwip->list == lwip) {
+
+                lwip->list = lwip->list->next;
+                netif_remove(&node->netif);
+                *interface_out = NULL;
+                delete node;
+            } else {
+                while (node->next != NULL && node->next != lwip) {
+                    node = node->next;
+                }
+                if (node->next != NULL && node->next == lwip) {
+                    Interface *remove = node->next;
+                    node->next = node->next->next;
+                    netif_remove(&remove->netif);
+                    *interface_out = NULL;
+                    delete remove;
+                }
+            }
+        }
+        osSemaphoreRelease(lwip->remove_interface);
+    }
+#endif
+}
+
+nsapi_error_t LWIP::remove_ethernet_interface(OnboardNetworkStack::Interface **interface_out)
+{
+#if LWIP_ETHERNET
+    LWIP::Interface *lwip = static_cast<Interface *>(*interface_out);
+    tcpip_callback_with_block((tcpip_callback_fn)&LWIP::Interface::delete_interface, interface_out, 1);
+    osSemaphoreAcquire(lwip->remove_interface, osWaitForever);
+    return NSAPI_ERROR_OK;
+#else
+    return NSAPI_ERROR_UNSUPPORTED;
+#endif //LWIP_ETHERNET
+}
 
 nsapi_error_t LWIP::add_l3ip_interface(L3IP &l3ip, bool default_if, OnboardNetworkStack::Interface **interface_out)
 {

features/lwipstack/LWIPStack.h

@@ -149,6 +149,7 @@ class LWIP : public OnboardNetworkStack, private mbed::NonCopyable<LWIP> {
         static void netif_link_irq(struct netif *netif);
         static void netif_status_irq(struct netif *netif);
         static Interface *our_if_from_netif(struct netif *netif);
+        static void delete_interface(OnboardNetworkStack::Interface **interface_out);
 
 #if LWIP_ETHERNET
         static err_t emac_low_level_output(struct netif *netif, struct pbuf *p);
@@ -208,6 +209,8 @@ class LWIP : public OnboardNetworkStack, private mbed::NonCopyable<LWIP> {
             void *hw; /**< alternative implementation pointer - used for PPP */
         };
 
+        mbed_rtos_storage_semaphore_t remove_interface_sem;
+        osSemaphoreId_t remove_interface;
         mbed_rtos_storage_semaphore_t linked_sem;
         osSemaphoreId_t linked;
         mbed_rtos_storage_semaphore_t unlinked_sem;
@@ -282,6 +285,14 @@ class LWIP : public OnboardNetworkStack, private mbed::NonCopyable<LWIP> {
      */
     virtual nsapi_error_t add_ppp_interface(PPP &ppp, bool default_if, OnboardNetworkStack::Interface **interface_out);
 
+    /** Remove a network interface from IP stack
+     *
+     * Removes layer 3 IP objects,network interface from stack list .
+     * @param[out] interface_out    pointer to stack interface object controlling the EMAC
+     * @return                      NSAPI_ERROR_OK on success, or error code
+     */
+    nsapi_error_t remove_ethernet_interface(OnboardNetworkStack::Interface **interface_out) override;
+
     /** Remove a network interface from IP stack
      *
      * Removes layer 3 IP objects,network interface from stack list, and shutdown device driver .

features/netsocket/OnboardNetworkStack.h

@@ -169,6 +169,11 @@ class OnboardNetworkStack : public NetworkStack {
         return NSAPI_ERROR_UNSUPPORTED;
     };
 
+    virtual nsapi_error_t remove_ethernet_interface(Interface **interface_out)
+    {
+        return NSAPI_ERROR_OK;
+    };
+
     virtual nsapi_error_t remove_l3ip_interface(Interface **interface_out)
     {
         return NSAPI_ERROR_OK;

features/netsocket/emac-drivers/TARGET_Cypress/COMPONENT_WHD/interface/WhdSTAInterface.cpp

@@ -359,6 +359,15 @@ nsapi_error_t WhdSTAInterface::disconnect()
     }
     whd_emac_wifi_link_state_changed(_whd_emac.ifp, WHD_FALSE);
 
+    // remove the interface added in connect
+    if (_interface) {
+        nsapi_error_t err = _stack.remove_ethernet_interface(&_interface);
+        if (err != NSAPI_ERROR_OK) {
+            return err;
+        }
+        _iface_shared.iface_sta = NULL;
+    }
+
     res = whd_wifi_deregister_event_handler(_whd_emac.ifp, sta_link_update_entry);
     if (res != WHD_SUCCESS) {
         return whd_toerror(res);

features/netsocket/emac-drivers/TARGET_Cypress/COMPONENT_WHD/interface/WhdSoftAPInterface.cpp

@@ -201,6 +201,15 @@ int WhdSoftAPInterface::stop(void)
     if (res != WHD_SUCCESS) {
         return whd_toerror(res);
     }
+
+    // remove the interface added in start
+    if (_interface) {
+        nsapi_error_t err = _stack.remove_ethernet_interface(&_interface);
+        if (err != NSAPI_ERROR_OK) {
+            return err;
+        }
+        _iface_shared.iface_softap = NULL;
+    }
     return NSAPI_ERROR_OK;
 }