Fix #71.

os/src/task/mod.rs

@@ -8,8 +8,9 @@ mod switch;
 #[allow(clippy::module_inception)]
 mod task;
 
+use self::id::TaskUserRes;
 use crate::fs::{open_file, OpenFlags};
-use alloc::sync::Arc;
+use alloc::{sync::Arc, vec::Vec};
 use lazy_static::*;
 use manager::fetch_task;
 use process::ProcessControlBlock;
@@ -90,12 +91,21 @@ pub fn exit_current_and_run_next(exit_code: i32) {
         // deallocate user res (including tid/trap_cx/ustack) of all threads
         // it has to be done before we dealloc the whole memory_set
         // otherwise they will be deallocated twice
+        let mut recycle_res = Vec::<TaskUserRes>::new();
         for task in process_inner.tasks.iter().filter(|t| t.is_some()) {
             let task = task.as_ref().unwrap();
             let mut task_inner = task.inner_exclusive_access();
-            task_inner.res = None;
+            if let Some(res) = task_inner.res.take() {
+                recycle_res.push(res);
+            }
         }
+        // dealloc_tid and dealloc_user_res require access to PCB inner, so we
+        // need to collect those user res first, then release process_inner
+        // for now to avoid deadlock/double borrow problem.
+        drop(process_inner);
+        recycle_res.clear();
 
+        let mut process_inner = process.inner_exclusive_access();
         process_inner.children.clear();
         // deallocate other data in user space i.e. program code/data section
         process_inner.memory_set.recycle_data_pages();