Merge release-20201030.0-53-g0fb5353e4 (automated)

2 files changed, 22 insertions, 13 deletions

diff --git a/pkg/sentry/kernel/shm/shm.go b/pkg/sentry/kernel/shm/shm.go
index ebbebf46b..92d60ba78 100644
--- a/pkg/sentry/kernel/shm/shm.go
+++ b/pkg/sentry/kernel/shm/shm.go
@@ -251,7 +251,7 @@ func (r *Registry) newShm(ctx context.Context, pid int32, key Key, creator fs.Fi
 		creatorPID:    pid,
 		changeTime:    ktime.NowFromContext(ctx),
 	}
-	shm.EnableLeakCheck()
+	shm.InitRefs()
 
 	// Find the next available ID.
 	for id := r.lastIDUsed + 1; id != r.lastIDUsed; id++ {
diff --git a/pkg/sentry/kernel/shm/shm_refs.go b/pkg/sentry/kernel/shm/shm_refs.go
index 5f148594c..82ca1ed06 100644
--- a/pkg/sentry/kernel/shm/shm_refs.go
+++ b/pkg/sentry/kernel/shm/shm_refs.go
@@ -20,9 +20,6 @@ var Shmobj *Shm
 // 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 ShmRefs struct {
 	// refCount is composed of two fields:
@@ -35,6 +32,13 @@ type ShmRefs struct {
 	refCount int64
 }
 
+// InitRefs initializes r with one reference and, if enabled, activates leak
+// checking.
+func (r *ShmRefs) InitRefs() {
+	atomic.StoreInt64(&r.refCount, 1)
+	refsvfs2.Register(r)
+}
+
 // RefType implements refsvfs2.CheckedObject.RefType.
 func (r *ShmRefs) RefType() string {
 	return fmt.Sprintf("%T", Shmobj)[1:]
@@ -58,8 +62,7 @@ func (r *ShmRefs) EnableLeakCheck() {
 // ReadRefs returns the current number of references. The returned count is
 // inherently racy and is unsafe to use without external synchronization.
 func (r *ShmRefs) ReadRefs() int64 {
-
-	return atomic.LoadInt64(&r.refCount) + 1
+	return atomic.LoadInt64(&r.refCount)
 }
 
 // IncRef implements refs.RefCounter.IncRef.
@@ -67,8 +70,10 @@ func (r *ShmRefs) ReadRefs() int64 {
 //go:nosplit
 func (r *ShmRefs) IncRef() {
 	v := atomic.AddInt64(&r.refCount, 1)
-	refsvfs2.LogIncRef(r, v+1)
-	if v <= 0 {
+	if ShmenableLogging {
+		refsvfs2.LogIncRef(r, v)
+	}
+	if v <= 1 {
 		panic(fmt.Sprintf("Incrementing non-positive count %p on %s", r, r.RefType()))
 	}
 }
@@ -82,14 +87,16 @@ func (r *ShmRefs) IncRef() {
 //go:nosplit
 func (r *ShmRefs) 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 {
 
 		atomic.AddInt64(&r.refCount, -speculativeRef)
 		return false
 	}
 
 	v := atomic.AddInt64(&r.refCount, -speculativeRef+1)
-	refsvfs2.LogTryIncRef(r, v+1)
+	if ShmenableLogging {
+		refsvfs2.LogTryIncRef(r, v)
+	}
 	return true
 }
 
@@ -107,12 +114,14 @@ func (r *ShmRefs) TryIncRef() bool {
 //go:nosplit
 func (r *ShmRefs) DecRef(destroy func()) {
 	v := atomic.AddInt64(&r.refCount, -1)
-	refsvfs2.LogDecRef(r, v+1)
+	if ShmenableLogging {
+		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)
 
 		if destroy != nil {