From 17c08ce26c0f318d8da489009a8cdd6ecb8f8511 Mon Sep 17 00:00:00 2001
From: Jiajie Chen <noc@jiegec.ac.cn>
Date: Mon, 11 Mar 2019 17:19:00 +0800
Subject: [PATCH] Fix sys_exit/sys_exit_group deadlock

---
 kernel/src/process/structs.rs |  7 -------
 kernel/src/syscall/proc.rs    | 29 ++++++++++++++++++++++++-----
 2 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/kernel/src/process/structs.rs b/kernel/src/process/structs.rs
index dc26a6e..8cca5a1 100644
--- a/kernel/src/process/structs.rs
+++ b/kernel/src/process/structs.rs
@@ -365,13 +365,6 @@ impl Process {
         }
         self.futexes.get(&uaddr).unwrap().clone()
     }
-    pub fn report_exit_to_parent(&mut self, exit_code: usize) {
-        if let Some(parent) = &self.parent {
-            let mut parent = parent.lock();
-            parent.child_exit_code.insert(self.pid.get(), exit_code);
-            parent.child_exit.notify_one();
-        }
-    }
 }
 
 
diff --git a/kernel/src/syscall/proc.rs b/kernel/src/syscall/proc.rs
index eabc6a1..851f8fd 100644
--- a/kernel/src/syscall/proc.rs
+++ b/kernel/src/syscall/proc.rs
@@ -179,11 +179,21 @@ pub fn sys_exit(exit_code: usize) -> ! {
     info!("exit: {}, code: {}", tid, exit_code);
     let mut proc = process();
     proc.threads.retain(|&id| id != tid);
-    if proc.threads.len() == 0 {
-        // last thread
-        proc.report_exit_to_parent(exit_code);
-    }
+
+    // for last thread,
+    // notify parent and fill exit code
+    // avoid deadlock
+    let exit = proc.threads.len() == 0;
+    let proc_parent = proc.parent.clone();
+    let pid = proc.pid.get();
     drop(proc);
+    if exit {
+        if let Some(parent) = proc_parent {
+            let mut parent = parent.lock();
+            parent.child_exit_code.insert(pid, exit_code);
+            parent.child_exit.notify_one();
+        }
+    }
 
     // perform futex wake 1
     // ref: http://man7.org/linux/man-pages/man2/set_tid_address.2.html
@@ -210,8 +220,17 @@ pub fn sys_exit_group(exit_code: usize) -> ! {
     for tid in proc.threads.iter() {
         processor().manager().exit(*tid, exit_code);
     }
-    proc.report_exit_to_parent(exit_code);
+
+    // notify parent and fill exit code
+    // avoid deadlock
+    let proc_parent = proc.parent.clone();
+    let pid = proc.pid.get();
     drop(proc);
+    if let Some(parent) = proc_parent {
+        let mut parent = parent.lock();
+        parent.child_exit_code.insert(pid, exit_code);
+        parent.child_exit.notify_one();
+    }
 
     processor().yield_now();
     unreachable!();