upcall: remove upcall client when stopping vm

In order to avoid resource leak, we need to remove upcall client in vm
and vcpu manager when stopping vm.

Signed-off-by: Chao Wu <chaowu@linux.alibaba.com>

src/dragonball/src/vm/mod.rs

@@ -492,6 +492,13 @@ impl Vm {
             .map_err(StopMicrovmError::DeviceManager)
     }
 
+    /// Remove upcall client when the VM is destoryed.
+    #[cfg(feature = "dbs-upcall")]
+    pub fn remove_upcall(&mut self) -> std::result::Result<(), StopMicrovmError> {
+        self.upcall_client = None;
+        Ok(())
+    }
+
     /// Reset the console into canonical mode.
     pub fn reset_console(&self) -> std::result::Result<(), DeviceMgrError> {
         self.device_manager.reset_console()

src/dragonball/src/vmm.rs

@@ -162,6 +162,11 @@ impl Vmm {
                     warn!("failed to remove devices: {:?}", e);
                 }
 
+                #[cfg(feature = "dbs-upcall")]
+                if let Err(e) = vm.remove_upcall() {
+                    warn!("failed to remove upcall: {:?}", e);
+                }
+
                 if let Err(e) = vm.reset_console() {
                     warn!("Cannot set canonical mode for the terminal. {:?}", e);
                 }
@@ -174,6 +179,8 @@ impl Vmm {
                         if let Err(e) = mgr.exit_all_vcpus() {
                             warn!("Failed to exit vcpu thread. {:?}", e);
                         }
+                        #[cfg(feature = "dbs-upcall")]
+                        mgr.set_upcall_channel(None);
                     }
                     Err(e) => warn!("Failed to get vcpu manager {:?}", e),
                 }