From ec906e46c0f99ab4d134c1d7bd84b48ea0a78488 Mon Sep 17 00:00:00 2001
From: Andrei Vagin <avagin@google.com>
Date: Mon, 22 Jul 2019 13:27:13 -0700
Subject: [PATCH] kvm: fix race between machine.Put and machine.Get

m.available.Signal() has to be called under m.mu.RLock, otherwise it can
race with machine.Get:

m.Get			| m.Put
-------------------------------------
m.mu.Lock()		|
Seatching available vcpu|
			| m.available.Signal()
m.available.Wait	|

PiperOrigin-RevId: 259394051
---
 pkg/sentry/platform/kvm/machine.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pkg/sentry/platform/kvm/machine.go b/pkg/sentry/platform/kvm/machine.go
index 679087e25..cc6c138b2 100644
--- a/pkg/sentry/platform/kvm/machine.go
+++ b/pkg/sentry/platform/kvm/machine.go
@@ -388,7 +388,10 @@ func (m *machine) Get() *vCPU {
 func (m *machine) Put(c *vCPU) {
 	c.unlock()
 	runtime.UnlockOSThread()
+
+	m.mu.RLock()
 	m.available.Signal()
+	m.mu.RUnlock()
 }
 
 // newDirtySet returns a new dirty set.