drivers/usbdev/cdcacm: Add a mutex around driver initialize / uninitialize

This protects the driver in case multiple threads are trying to initialize
or uninitialize the cdcacm concurrently.

Note that this only protects the case when the private pointer is not managed
outside the kernel. If someone has acquired the pointer to the driver and uses
that, it also needs to manage the protection itself if needed.

Signed-off-by: Jukka Laitinen <jukka.laitinen@tii.ae>

drivers/usbdev/cdcacm.c

@@ -313,6 +313,10 @@ static const struct uart_ops_s g_uartops =
   cdcuart_sendbuf        /* sendbuf */
 };
 
+/* Mutex to protect device initialization / uninitialization*****************/
+
+static mutex_t g_init_lock = NXMUTEX_INITIALIZER;
+
 /****************************************************************************
  * Private Functions
  ****************************************************************************/
@@ -3377,9 +3381,16 @@ int cdcacm_initialize(int minor, FAR void **handle)
   devinfo.epno[CDCACM_EP_BULKIN_IDX]  = CONFIG_CDCACM_EPBULKIN;
   devinfo.epno[CDCACM_EP_BULKOUT_IDX] = CONFIG_CDCACM_EPBULKOUT;
 
+  ret = nxmutex_lock(&g_init_lock);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
   /* Get an instance of the serial driver class object */
 
   ret = cdcacm_classobject(minor, &devinfo, &drvr);
+
   if (ret == OK)
     {
       /* Register the USB serial class driver */
@@ -3392,6 +3403,8 @@ int cdcacm_initialize(int minor, FAR void **handle)
         }
     }
 
+  nxmutex_unlock(&g_init_lock);
+
   /* Return the driver instance (if any) if the caller has requested it
    * by provided a pointer to the location to return it.
    */
@@ -3460,6 +3473,12 @@ int cdcacm_uninitialize_instance(int minor,
 
   snprintf(devname, sizeof(devname), CDCACM_DEVNAME_FORMAT, minor);
 
+  ret = nxmutex_lock(&g_init_lock);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
   /* If classdev is not provided, find it from the file system */
 
   if (classdev == NULL)
@@ -3472,7 +3491,8 @@ int cdcacm_uninitialize_instance(int minor,
         }
       else
         {
-          return -ENODEV;
+          ret = -ENODEV;
+          goto out;
         }
     }
 
@@ -3502,6 +3522,8 @@ int cdcacm_uninitialize_instance(int minor,
                (uint16_t)-ret);
     }
 
+out:
+  nxmutex_unlock(&g_init_lock);
   return ret;
 }