From 45566fa4e4bc55e870ae1d7f80778be8432bdef5 Mon Sep 17 00:00:00 2001
From: Ian Gudger <igudger@google.com>
Date: Fri, 28 Jun 2019 20:06:33 -0700
Subject: Add finalizer on AtomicRefCount to check for leaks.

PiperOrigin-RevId: 255711454
---
 pkg/refs/BUILD         |  3 +++
 pkg/refs/refcounter.go | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

(limited to 'pkg/refs')

diff --git a/pkg/refs/BUILD b/pkg/refs/BUILD
index 0652fbbe6..9c08452fc 100644
--- a/pkg/refs/BUILD
+++ b/pkg/refs/BUILD
@@ -24,6 +24,9 @@ go_library(
     ],
     importpath = "gvisor.dev/gvisor/pkg/refs",
     visibility = ["//:sandbox"],
+    deps = [
+        "//pkg/log",
+    ],
 )
 
 go_test(
diff --git a/pkg/refs/refcounter.go b/pkg/refs/refcounter.go
index 20f515391..6d6c3a782 100644
--- a/pkg/refs/refcounter.go
+++ b/pkg/refs/refcounter.go
@@ -18,8 +18,11 @@ package refs
 
 import (
 	"reflect"
+	"runtime"
 	"sync"
 	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/log"
 )
 
 // RefCounter is the interface to be implemented by objects that are reference
@@ -189,6 +192,11 @@ type AtomicRefCount struct {
 	// how these fields are used.
 	refCount int64
 
+	// name is the name of the type which owns this ref count.
+	//
+	// name is immutable after EnableLeakCheck is called.
+	name string
+
 	// mu protects the list below.
 	mu sync.Mutex `state:"nosave"`
 
@@ -196,6 +204,67 @@ type AtomicRefCount struct {
 	weakRefs weakRefList `state:"nosave"`
 }
 
+// LeakMode configures the leak checker.
+type LeakMode uint32
+
+const (
+	// uninitializedLeakChecking indicates that the leak checker has not yet been initialized.
+	uninitializedLeakChecking LeakMode = iota
+
+	// NoLeakChecking indicates that no effort should be made to check for
+	// leaks.
+	NoLeakChecking
+
+	// LeaksLogWarning indicates that a warning should be logged when leaks
+	// are found.
+	LeaksLogWarning
+)
+
+// leakMode stores the current mode for the reference leak checker.
+//
+// Values must be one of the LeakMode values.
+//
+// leakMode must be accessed atomically.
+var leakMode uint32
+
+// SetLeakMode configures the reference leak checker.
+func SetLeakMode(mode LeakMode) {
+	atomic.StoreUint32(&leakMode, uint32(mode))
+}
+
+func (r *AtomicRefCount) finalize() {
+	var note string
+	switch LeakMode(atomic.LoadUint32(&leakMode)) {
+	case NoLeakChecking:
+		return
+	case uninitializedLeakChecking:
+		note = "(Leak checker uninitialized): "
+	}
+	if n := r.ReadRefs(); n != 0 {
+		log.Warningf("%sAtomicRefCount %p owned by %q garbage collected with ref count of %d (want 0)", note, r, r.name, n)
+	}
+}
+
+// EnableLeakCheck checks for reference leaks when the AtomicRefCount gets
+// garbage collected.
+//
+// This function adds a finalizer to the AtomicRefCount, so the AtomicRefCount
+// must be at the beginning of its parent.
+//
+// name is a friendly name that will be listed as the owner of the
+// AtomicRefCount in logs. It should be the name of the parent type, including
+// package.
+func (r *AtomicRefCount) EnableLeakCheck(name string) {
+	if name == "" {
+		panic("invalid name")
+	}
+	if LeakMode(atomic.LoadUint32(&leakMode)) == NoLeakChecking {
+		return
+	}
+	r.name = name
+	runtime.SetFinalizer(r, (*AtomicRefCount).finalize)
+}
+
 // ReadRefs returns the current number of references. The returned count is
 // inherently racy and is unsafe to use without external synchronization.
 func (r *AtomicRefCount) ReadRefs() int64 {
-- 
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