3 files changed, 146 insertions, 5 deletions
diff --git a/pkg/tcpip/link/tun/device.go b/pkg/tcpip/link/tun/device.go
index 3b1510a33..b6ddbe81e 100644
--- a/pkg/tcpip/link/tun/device.go
+++ b/pkg/tcpip/link/tun/device.go
@@ -19,7 +19,6 @@ import (
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -135,6 +134,7 @@ func attachOrCreateNIC(s *stack.Stack, name, prefix string, linkCaps stack.LinkE
 
 		// 2. Creating a new NIC.
 		id := tcpip.NICID(s.UniqueID())
+		// TODO(gvisor.dev/1486): enable leak check for tunEndpoint.
 		endpoint := &tunEndpoint{
 			Endpoint: channel.New(defaultDevOutQueueLen, defaultDevMtu, ""),
 			stack:    s,
@@ -331,19 +331,18 @@ func (d *Device) WriteNotify() {
 // It is ref-counted as multiple opening files can attach to the same NIC.
 // The last owner is responsible for deleting the NIC.
 type tunEndpoint struct {
+	tunEndpointRefs
 	*channel.Endpoint
 
-	refs.AtomicRefCount
-
 	stack *stack.Stack
 	nicID tcpip.NICID
 	name  string
 	isTap bool
 }
 
-// DecRef decrements refcount of e, removes NIC if refcount goes to 0.
+// DecRef decrements refcount of e, removing NIC if it reaches 0.
 func (e *tunEndpoint) DecRef(ctx context.Context) {
-	e.DecRefWithDestructor(ctx, func(context.Context) {
+	e.tunEndpointRefs.DecRef(func() {
 		e.stack.RemoveNIC(e.nicID)
 	})
 }
diff --git a/pkg/tcpip/link/tun/tun_endpoint_refs.go b/pkg/tcpip/link/tun/tun_endpoint_refs.go
new file mode 100644
index 000000000..e0595429c
--- /dev/null
+++ b/pkg/tcpip/link/tun/tun_endpoint_refs.go
@@ -0,0 +1,118 @@
+package tun
+
+import (
+	"fmt"
+	"runtime"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/log"
+	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
+)
+
+// ownerType is used to customize logging. Note that we use a pointer to T so
+// that we do not copy the entire object when passed as a format parameter.
+var tunEndpointownerType *tunEndpoint
+
+// Refs implements refs.RefCounter. It keeps a reference count using atomic
+// operations and calls the destructor when the count reaches zero.
+//
+// Note that the number of references is actually refCount + 1 so that a default
+// zero-value Refs object contains one reference.
+//
+// TODO(gvisor.dev/issue/1486): Store stack traces when leak check is enabled in
+// a map with 16-bit hashes, and store the hash in the top 16 bits of refCount.
+// This will allow us to add stack trace information to the leak messages
+// without growing the size of Refs.
+//
+// +stateify savable
+type tunEndpointRefs struct {
+	// refCount is composed of two fields:
+	//
+	//	[32-bit speculative references]:[32-bit real references]
+	//
+	// Speculative references are used for TryIncRef, to avoid a CompareAndSwap
+	// loop. See IncRef, DecRef and TryIncRef for details of how these fields are
+	// used.
+	refCount int64
+}
+
+func (r *tunEndpointRefs) finalize() {
+	var note string
+	switch refs_vfs1.GetLeakMode() {
+	case refs_vfs1.NoLeakChecking:
+		return
+	case refs_vfs1.UninitializedLeakChecking:
+		note = "(Leak checker uninitialized): "
+	}
+	if n := r.ReadRefs(); n != 0 {
+		log.Warningf("%sRefs %p owned by %T garbage collected with ref count of %d (want 0)", note, r, tunEndpointownerType, n)
+	}
+}
+
+// EnableLeakCheck checks for reference leaks when Refs gets garbage collected.
+func (r *tunEndpointRefs) EnableLeakCheck() {
+	if refs_vfs1.GetLeakMode() != refs_vfs1.NoLeakChecking {
+		runtime.SetFinalizer(r, (*tunEndpointRefs).finalize)
+	}
+}
+
+// ReadRefs returns the current number of references. The returned count is
+// inherently racy and is unsafe to use without external synchronization.
+func (r *tunEndpointRefs) ReadRefs() int64 {
+
+	return atomic.LoadInt64(&r.refCount) + 1
+}
+
+// IncRef implements refs.RefCounter.IncRef.
+//
+//go:nosplit
+func (r *tunEndpointRefs) IncRef() {
+	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
+		panic(fmt.Sprintf("Incrementing non-positive ref count %p owned by %T", r, tunEndpointownerType))
+	}
+}
+
+// TryIncRef implements refs.RefCounter.TryIncRef.
+//
+// To do this safely without a loop, a speculative reference is first acquired
+// on the object. This allows multiple concurrent TryIncRef calls to distinguish
+// other TryIncRef calls from genuine references held.
+//
+//go:nosplit
+func (r *tunEndpointRefs) TryIncRef() bool {
+	const speculativeRef = 1 << 32
+	v := atomic.AddInt64(&r.refCount, speculativeRef)
+	if int32(v) < 0 {
+
+		atomic.AddInt64(&r.refCount, -speculativeRef)
+		return false
+	}
+
+	atomic.AddInt64(&r.refCount, -speculativeRef+1)
+	return true
+}
+
+// DecRef implements refs.RefCounter.DecRef.
+//
+// Note that speculative references are counted here. Since they were added
+// prior to real references reaching zero, they will successfully convert to
+// real references. In other words, we see speculative references only in the
+// following case:
+//
+//	A: TryIncRef [speculative increase => sees non-negative references]
+//	B: DecRef [real decrease]
+//	A: TryIncRef [transform speculative to real]
+//
+//go:nosplit
+func (r *tunEndpointRefs) DecRef(destroy func()) {
+	switch v := atomic.AddInt64(&r.refCount, -1); {
+	case v < -1:
+		panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %T", r, tunEndpointownerType))
+
+	case v == -1:
+
+		if destroy != nil {
+			destroy()
+		}
+	}
+}
diff --git a/pkg/tcpip/link/tun/tun_state_autogen.go b/pkg/tcpip/link/tun/tun_state_autogen.go
index 7f75aef19..0b3041e84 100644
--- a/pkg/tcpip/link/tun/tun_state_autogen.go
+++ b/pkg/tcpip/link/tun/tun_state_autogen.go
@@ -36,6 +36,30 @@ func (x *Device) StateLoad(m state.Source) {
 	m.Load(3, &x.flags)
 }
 
+func (x *tunEndpointRefs) StateTypeName() string {
+	return "pkg/tcpip/link/tun.tunEndpointRefs"
+}
+
+func (x *tunEndpointRefs) StateFields() []string {
+	return []string{
+		"refCount",
+	}
+}
+
+func (x *tunEndpointRefs) beforeSave() {}
+
+func (x *tunEndpointRefs) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.refCount)
+}
+
+func (x *tunEndpointRefs) afterLoad() {}
+
+func (x *tunEndpointRefs) StateLoad(m state.Source) {
+	m.Load(0, &x.refCount)
+}
+
 func init() {
 	state.Register((*Device)(nil))
+	state.Register((*tunEndpointRefs)(nil))
 }