note potential lost wakeup problem in Condvar. fix some use case.

kernel/src/fs/stdio.rs

@@ -30,10 +30,12 @@ impl Stdin {
         }
         #[cfg(not(feature = "board_k210"))]
         loop {
-            let ret = self.buf.lock().pop_front();
-            match ret {
+            let mut buf_lock = self.buf.lock();
+            match buf_lock.pop_front() {
                 Some(c) => return c,
-                None => self.pushed._wait(),
+                None => {
+                    self.pushed.wait(buf_lock);
+                }
             }
         }
     }

kernel/src/net/structs.rs

@@ -265,9 +265,8 @@ impl Socket for TcpSocketState {
                             TcpState::SynSent => {
                                 // still connecting
                                 drop(socket);
-                                drop(sockets);
                                 debug!("poll for connection wait");
-                                SOCKET_ACTIVITY._wait();
+                                SOCKET_ACTIVITY.wait(sockets);
                             }
                             TcpState::Established => {
                                 break Ok(0);
@@ -357,10 +356,8 @@ impl Socket for TcpSocketState {
                 return Ok((new_socket, Endpoint::Ip(remote_endpoint)));
             }
 
-            // avoid deadlock
             drop(socket);
-            drop(sockets);
-            SOCKET_ACTIVITY._wait();
+            SOCKET_ACTIVITY.wait(sockets);
         }
     }
 
@@ -447,9 +444,8 @@ impl Socket for UdpSocketState {
                 );
             }
 
-            // avoid deadlock
             drop(socket);
-            SOCKET_ACTIVITY._wait()
+            SOCKET_ACTIVITY.wait(sockets);
         }
     }
 
@@ -626,10 +622,8 @@ impl Socket for RawSocketState {
                 );
             }
 
-            // avoid deadlock
             drop(socket);
-            drop(sockets);
-            SOCKET_ACTIVITY._wait()
+            SOCKET_ACTIVITY.wait(sockets);
         }
     }
 

kernel/src/sync/condvar.rs

@@ -15,6 +15,7 @@ impl Condvar {
     }
 
     /// Park current thread and wait for this condvar to be notified.
+    #[deprecated(note = "this may leads to lost wakeup problem. please use `wait` instead.")]
     pub fn _wait(&self) {
         // The condvar might be notified between adding to queue and thread parking.
         // So park current thread before wait queue lock is freed.
@@ -25,6 +26,7 @@ impl Condvar {
         });
     }
 
+    #[deprecated(note = "this may leads to lost wakeup problem. please use `wait` instead.")]
     pub fn wait_any(condvars: &[&Condvar]) {
         let token = Arc::new(thread::current());
         // Avoid racing in the same way as the function above
@@ -40,19 +42,23 @@ impl Condvar {
         });
     }
 
-    pub fn add_to_wait_queue(&self) -> MutexGuard<VecDeque<Arc<thread::Thread>>, SpinNoIrq> {
+    fn add_to_wait_queue(&self) -> MutexGuard<VecDeque<Arc<thread::Thread>>, SpinNoIrq> {
         let mut lock = self.wait_queue.lock();
         lock.push_back(Arc::new(thread::current()));
         return lock;
     }
 
+    /// Park current thread and wait for this condvar to be notified.
     pub fn wait<'a, T, S>(&self, guard: MutexGuard<'a, T, S>) -> MutexGuard<'a, T, S>
     where
         S: MutexSupport,
     {
         let mutex = guard.mutex;
+        let lock = self.add_to_wait_queue();
+        thread::park_action(move || {
+            drop(lock);
             drop(guard);
-        self._wait();
+        });
         mutex.lock()
     }
 
@@ -80,7 +86,4 @@ impl Condvar {
         }
         count
     }
-    pub fn _clear(&self) {
-        self.wait_queue.lock().clear();
-    }
 }

kernel/src/syscall/misc.rs

@@ -91,6 +91,7 @@ pub fn sys_futex(uaddr: usize, op: u32, val: i32, timeout: *const TimeSpec) -> S
                 return Err(SysError::EAGAIN);
             }
             // FIXME: support timeout
+            // FIXME: fix racing
             queue._wait();
             Ok(0)
         }

kernel/src/syscall/proc.rs

@@ -120,8 +120,7 @@ pub fn sys_wait4(pid: isize, wstatus: *mut i32) -> SysResult {
             target
         );
         let condvar = proc.child_exit.clone();
-        drop(proc); // must release lock of current process
-        condvar._wait();
+        condvar.wait(proc);
     }
 }