6 files changed, 165 insertions, 16 deletions

diff --git a/pkg/sentry/socket/unix/socket_refs.go b/pkg/sentry/socket/unix/socket_refs.go
index 4c6ec186b..dababb85f 100644
--- a/pkg/sentry/socket/unix/socket_refs.go
+++ b/pkg/sentry/socket/unix/socket_refs.go
@@ -1,6 +1,7 @@
 package unix
 
 import (
+	"fmt"
 	"runtime"
 	"sync/atomic"
 
@@ -18,6 +19,11 @@ var socketOpsCommonownerType *socketOpsCommon
 // 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 socketOpsCommonRefs struct {
 	// refCount is composed of two fields:
@@ -62,7 +68,7 @@ func (r *socketOpsCommonRefs) ReadRefs() int64 {
 //go:nosplit
 func (r *socketOpsCommonRefs) IncRef() {
 	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
-		panic("Incrementing non-positive ref count")
+		panic(fmt.Sprintf("Incrementing non-positive ref count %p owned by %T", r, socketOpsCommonownerType))
 	}
 }
 
@@ -101,7 +107,7 @@ func (r *socketOpsCommonRefs) TryIncRef() bool {
 func (r *socketOpsCommonRefs) DecRef(destroy func()) {
 	switch v := atomic.AddInt64(&r.refCount, -1); {
 	case v < -1:
-		panic("Decrementing non-positive ref count")
+		panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %T", r, socketOpsCommonownerType))
 
 	case v == -1:
 
diff --git a/pkg/sentry/socket/unix/transport/connectioned.go b/pkg/sentry/socket/unix/transport/connectioned.go
index c67b602f0..e3a75b519 100644
--- a/pkg/sentry/socket/unix/transport/connectioned.go
+++ b/pkg/sentry/socket/unix/transport/connectioned.go
@@ -142,9 +142,9 @@ func NewPair(ctx context.Context, stype linux.SockType, uid UniqueIDProvider) (E
 	}
 
 	q1 := &queue{ReaderQueue: a.Queue, WriterQueue: b.Queue, limit: initialLimit}
-	q1.EnableLeakCheck("transport.queue")
+	q1.EnableLeakCheck()
 	q2 := &queue{ReaderQueue: b.Queue, WriterQueue: a.Queue, limit: initialLimit}
-	q2.EnableLeakCheck("transport.queue")
+	q2.EnableLeakCheck()
 
 	if stype == linux.SOCK_STREAM {
 		a.receiver = &streamQueueReceiver{queueReceiver: queueReceiver{q1}}
@@ -300,14 +300,14 @@ func (e *connectionedEndpoint) BidirectionalConnect(ctx context.Context, ce Conn
 	}
 
 	readQueue := &queue{ReaderQueue: ce.WaiterQueue(), WriterQueue: ne.Queue, limit: initialLimit}
-	readQueue.EnableLeakCheck("transport.queue")
+	readQueue.EnableLeakCheck()
 	ne.connected = &connectedEndpoint{
 		endpoint:   ce,
 		writeQueue: readQueue,
 	}
 
 	writeQueue := &queue{ReaderQueue: ne.Queue, WriterQueue: ce.WaiterQueue(), limit: initialLimit}
-	writeQueue.EnableLeakCheck("transport.queue")
+	writeQueue.EnableLeakCheck()
 	if e.stype == linux.SOCK_STREAM {
 		ne.receiver = &streamQueueReceiver{queueReceiver: queueReceiver{readQueue: writeQueue}}
 	} else {
diff --git a/pkg/sentry/socket/unix/transport/connectionless.go b/pkg/sentry/socket/unix/transport/connectionless.go
index 70ee8f9b8..4751b2fd8 100644
--- a/pkg/sentry/socket/unix/transport/connectionless.go
+++ b/pkg/sentry/socket/unix/transport/connectionless.go
@@ -42,7 +42,7 @@ var (
 func NewConnectionless(ctx context.Context) Endpoint {
 	ep := &connectionlessEndpoint{baseEndpoint{Queue: &waiter.Queue{}}}
 	q := queue{ReaderQueue: ep.Queue, WriterQueue: &waiter.Queue{}, limit: initialLimit}
-	q.EnableLeakCheck("transport.queue")
+	q.EnableLeakCheck()
 	ep.receiver = &queueReceiver{readQueue: &q}
 	return ep
 }
diff --git a/pkg/sentry/socket/unix/transport/queue.go b/pkg/sentry/socket/unix/transport/queue.go
index ef6043e19..342def28f 100644
--- a/pkg/sentry/socket/unix/transport/queue.go
+++ b/pkg/sentry/socket/unix/transport/queue.go
@@ -16,7 +16,6 @@ package transport
 
 import (
 	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserr"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -28,7 +27,7 @@ import (
 //
 // +stateify savable
 type queue struct {
-	refs.AtomicRefCount
+	queueRefs
 
 	ReaderQueue *waiter.Queue
 	WriterQueue *waiter.Queue
@@ -68,11 +67,13 @@ func (q *queue) Reset(ctx context.Context) {
 	q.mu.Unlock()
 }
 
-// DecRef implements RefCounter.DecRef with destructor q.Reset.
+// DecRef implements RefCounter.DecRef.
 func (q *queue) DecRef(ctx context.Context) {
-	q.DecRefWithDestructor(ctx, q.Reset)
-	// We don't need to notify after resetting because no one cares about
-	// this queue after all references have been dropped.
+	q.queueRefs.DecRef(func() {
+		// We don't need to notify after resetting because no one cares about
+		// this queue after all references have been dropped.
+		q.Reset(ctx)
+	})
 }
 
 // IsReadable determines if q is currently readable.
diff --git a/pkg/sentry/socket/unix/transport/queue_refs.go b/pkg/sentry/socket/unix/transport/queue_refs.go
new file mode 100644
index 000000000..0d4e34988
--- /dev/null
+++ b/pkg/sentry/socket/unix/transport/queue_refs.go
@@ -0,0 +1,118 @@
+package transport
+
+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 queueownerType *queue
+
+// 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 queueRefs 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 *queueRefs) 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, queueownerType, n)
+	}
+}
+
+// EnableLeakCheck checks for reference leaks when Refs gets garbage collected.
+func (r *queueRefs) EnableLeakCheck() {
+	if refs_vfs1.GetLeakMode() != refs_vfs1.NoLeakChecking {
+		runtime.SetFinalizer(r, (*queueRefs).finalize)
+	}
+}
+
+// ReadRefs returns the current number of references. The returned count is
+// inherently racy and is unsafe to use without external synchronization.
+func (r *queueRefs) ReadRefs() int64 {
+
+	return atomic.LoadInt64(&r.refCount) + 1
+}
+
+// IncRef implements refs.RefCounter.IncRef.
+//
+//go:nosplit
+func (r *queueRefs) IncRef() {
+	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
+		panic(fmt.Sprintf("Incrementing non-positive ref count %p owned by %T", r, queueownerType))
+	}
+}
+
+// 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 *queueRefs) 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 *queueRefs) 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, queueownerType))
+
+	case v == -1:
+
+		if destroy != nil {
+			destroy()
+		}
+	}
+}
diff --git a/pkg/sentry/socket/unix/transport/transport_state_autogen.go b/pkg/sentry/socket/unix/transport/transport_state_autogen.go
index 4b88ea3ae..91e632833 100644
--- a/pkg/sentry/socket/unix/transport/transport_state_autogen.go
+++ b/pkg/sentry/socket/unix/transport/transport_state_autogen.go
@@ -71,7 +71,7 @@ func (x *queue) StateTypeName() string {
 
 func (x *queue) StateFields() []string {
 	return []string{
-		"AtomicRefCount",
+		"queueRefs",
 		"ReaderQueue",
 		"WriterQueue",
 		"closed",
@@ -86,7 +86,7 @@ func (x *queue) beforeSave() {}
 
 func (x *queue) StateSave(m state.Sink) {
 	x.beforeSave()
-	m.Save(0, &x.AtomicRefCount)
+	m.Save(0, &x.queueRefs)
 	m.Save(1, &x.ReaderQueue)
 	m.Save(2, &x.WriterQueue)
 	m.Save(3, &x.closed)
@@ -99,7 +99,7 @@ func (x *queue) StateSave(m state.Sink) {
 func (x *queue) afterLoad() {}
 
 func (x *queue) StateLoad(m state.Source) {
-	m.Load(0, &x.AtomicRefCount)
+	m.Load(0, &x.queueRefs)
 	m.Load(1, &x.ReaderQueue)
 	m.Load(2, &x.WriterQueue)
 	m.Load(3, &x.closed)
@@ -109,6 +109,29 @@ func (x *queue) StateLoad(m state.Source) {
 	m.Load(7, &x.dataList)
 }
 
+func (x *queueRefs) StateTypeName() string {
+	return "pkg/sentry/socket/unix/transport.queueRefs"
+}
+
+func (x *queueRefs) StateFields() []string {
+	return []string{
+		"refCount",
+	}
+}
+
+func (x *queueRefs) beforeSave() {}
+
+func (x *queueRefs) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.refCount)
+}
+
+func (x *queueRefs) afterLoad() {}
+
+func (x *queueRefs) StateLoad(m state.Source) {
+	m.Load(0, &x.refCount)
+}
+
 func (x *messageList) StateTypeName() string {
 	return "pkg/sentry/socket/unix/transport.messageList"
 }
@@ -339,6 +362,7 @@ func init() {
 	state.Register((*connectionedEndpoint)(nil))
 	state.Register((*connectionlessEndpoint)(nil))
 	state.Register((*queue)(nil))
+	state.Register((*queueRefs)(nil))
 	state.Register((*messageList)(nil))
 	state.Register((*messageEntry)(nil))
 	state.Register((*ControlMessages)(nil))