[lxc-devel] [lxd/master] QMP: Fix race in Disconnect

[tomponline on Github]

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From 32fbbdcc9ddd9738b1eff6935e496d2d31ff6da1 Mon Sep 17 00:00:00 2001
From: Thomas Parrott <thomas.parrott at canonical.com>
Date: Mon, 4 Jan 2021 14:53:24 +0000
Subject: [PATCH] lxd/instance/drivers/qmp: Fix race in Disconnect

Can end up calling close() on the chDisconnect channel multiple times if called concurrently.

Fixes #8294

Signed-off-by: Thomas Parrott <thomas.parrott at canonical.com>
---
 lxd/instance/drivers/qmp/monitor.go | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/lxd/instance/drivers/qmp/monitor.go b/lxd/instance/drivers/qmp/monitor.go
index 00d2453ad0..72950e093c 100644
--- a/lxd/instance/drivers/qmp/monitor.go
+++ b/lxd/instance/drivers/qmp/monitor.go
@@ -171,16 +171,17 @@ func (m *Monitor) Wait() (chan struct{}, error) {
 
 // Disconnect forces a disconnection from QEMU.
 func (m *Monitor) Disconnect() {
+	// Remove from the map.
+	monitorsLock.Lock()
+	defer monitorsLock.Unlock()
+
 	// Stop all go routines and disconnect from socket.
 	if !m.disconnected {
 		close(m.chDisconnect)
+		m.disconnected = true
+		m.qmp.Disconnect()
 	}
-	m.disconnected = true
-	m.qmp.Disconnect()
 
-	// Remove from the map.
-	monitorsLock.Lock()
-	defer monitorsLock.Unlock()
 	delete(monitors, m.path)
 }