Initialize references with a value of 1.

This lets us avoid treating a value of 0 as one reference. All references
using the refsvfs2 template must call InitRefs() before the reference is
incremented/decremented, or else a panic will occur. Therefore, it should be
pretty easy to identify missing InitRef calls during testing.

Updates #1486.

PiperOrigin-RevId: 341411151

1 files changed, 22 insertions, 16 deletions

diff --git a/pkg/refsvfs2/refs_template.go b/pkg/refsvfs2/refs_template.go
index 8f50b4ee6..f64b6c6ae 100644
--- a/pkg/refsvfs2/refs_template.go
+++ b/pkg/refsvfs2/refs_template.go
@@ -13,10 +13,7 @@
 // limitations under the License.
 
 // Package refs_template defines a template that can be used by reference
-// counted objects. The "owner" template parameter is used in log messages to
-// indicate the type of reference-counted object that exhibited a reference
-// leak. As a result, structs that are embedded in other structs should not use
-// this template, since it will make tracking down leaks more difficult.
+// counted objects.
 package refs_template
 
 import (
@@ -43,9 +40,6 @@ var obj *T
 // 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.
-//
 // +stateify savable
 type Refs struct {
 	// refCount is composed of two fields:
@@ -58,6 +52,13 @@ type Refs struct {
 	refCount int64
 }
 
+// InitRefs initializes r with one reference and, if enabled, activates leak
+// checking.
+func (r *Refs) InitRefs() {
+	atomic.StoreInt64(&r.refCount, 1)
+	refsvfs2.Register(r)
+}
+
 // RefType implements refsvfs2.CheckedObject.RefType.
 func (r *Refs) RefType() string {
 	return fmt.Sprintf("%T", obj)[1:]
@@ -81,8 +82,7 @@ func (r *Refs) EnableLeakCheck() {
 // ReadRefs returns the current number of references. The returned count is
 // inherently racy and is unsafe to use without external synchronization.
 func (r *Refs) ReadRefs() int64 {
-	// Account for the internal -1 offset on refcounts.
-	return atomic.LoadInt64(&r.refCount) + 1
+	return atomic.LoadInt64(&r.refCount)
 }
 
 // IncRef implements refs.RefCounter.IncRef.
@@ -90,8 +90,10 @@ func (r *Refs) ReadRefs() int64 {
 //go:nosplit
 func (r *Refs) IncRef() {
 	v := atomic.AddInt64(&r.refCount, 1)
-	refsvfs2.LogIncRef(r, v+1)
-	if v <= 0 {
+	if enableLogging {
+		refsvfs2.LogIncRef(r, v)
+	}
+	if v <= 1 {
 		panic(fmt.Sprintf("Incrementing non-positive count %p on %s", r, r.RefType()))
 	}
 }
@@ -105,7 +107,7 @@ func (r *Refs) IncRef() {
 //go:nosplit
 func (r *Refs) TryIncRef() bool {
 	const speculativeRef = 1 << 32
-	if v := atomic.AddInt64(&r.refCount, speculativeRef); int32(v) < 0 {
+	if v := atomic.AddInt64(&r.refCount, speculativeRef); int32(v) == 0 {
 		// This object has already been freed.
 		atomic.AddInt64(&r.refCount, -speculativeRef)
 		return false
@@ -113,7 +115,9 @@ func (r *Refs) TryIncRef() bool {
 
 	// Turn into a real reference.
 	v := atomic.AddInt64(&r.refCount, -speculativeRef+1)
-	refsvfs2.LogTryIncRef(r, v+1)
+	if enableLogging {
+		refsvfs2.LogTryIncRef(r, v)
+	}
 	return true
 }
 
@@ -131,12 +135,14 @@ func (r *Refs) TryIncRef() bool {
 //go:nosplit
 func (r *Refs) DecRef(destroy func()) {
 	v := atomic.AddInt64(&r.refCount, -1)
-	refsvfs2.LogDecRef(r, v+1)
+	if enableLogging {
+		refsvfs2.LogDecRef(r, v+1)
+	}
 	switch {
-	case v < -1:
+	case v < 0:
 		panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %s", r, r.RefType()))
 
-	case v == -1:
+	case v == 0:
 		refsvfs2.Unregister(r)
 		// Call the destructor.
 		if destroy != nil {