Jiachen Lu created SSHD-1341:
--------------------------------
Summary: Deadlock in old version of SSHD
Key: SSHD-1341
URL: https://issues.apache.org/jira/browse/SSHD-1341
Project: MINA SSHD
Issue Type: Question
Affects Versions: 0.14.0
Reporter: Jiachen Lu
Attachments: image-2024-06-16-21-16-19-706.png,
image-2024-06-16-21-16-41-229.png
# SSHD Deadlock
## In a nutshell
I used some static analysis tools to discover a potential deadlock in version
0.14.x of mina-sshd. I would like to know if it is a false positive.
The related lock objects and trace are shown below.
I look forward to the community's assistance in confirming this issue. Thank
you for your response. If you need more information, please feel free to
contact me.
This deadlock might be similar to
[SSHD-966](https://issues.apache.org/jira/browse/SSHD-966).
## Deadlock Pair
Deadlock `synchronized void flush() throws IOException` (Trace 1) and
`synchronized (encodeLock)` (Trace 2) acquire locks `this` in class
`ChannelOutputStream` and `encodeLock` in reverse orders.
./sshd-core/src/main/java/org/apache/sshd/common/session/AbstractSession.java
```java
551 protected IoWriteFuture doWritePacket(Buffer buffer) throws IOException {
552 // Synchronize all write requests as needed by the encoding algorithm
553 // and also queue the write request in this synchronized block to
ensure
554 // packets are sent in the correct order
555 > synchronized (encodeLock) {
556 encode(buffer);
557 return ioSession.write(buffer);
558 }
559 }
```
Deadlock `synchronized void flush() throws IOException` (Trace 1) and
`synchronized (encodeLock)` (Trace 2) acquire locks `this` in class
`ChannelOutputStream` and `encodeLock` in reverse orders.
./sshd-core/src/main/java/org/apache/sshd/common/forward/TcpipServerChannel.java
```java
113 public void messageReceived(IoSession session, Readable message)
throws Exception {
114 if (isClosing()) {
115 log.debug("Ignoring write to channel {} in CLOSING
state", id);
116 } else {
117 Buffer buffer = new Buffer();
118 buffer.putBuffer(message);
119 out.write(buffer.array(), buffer.rpos(),
buffer.available());
120 > out.flush();
121 }
122 }
```
## Trace
### Trace1
!image-2024-06-16-21-16-19-706.png!
### Trace2
!image-2024-06-16-21-16-41-229.png!
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