Use new reference count utility throughout gvisor.

This uses the refs_vfs2 template in vfs2 as well as objects common to vfs1 and
vfs2. Note that vfs1-only refcounts are not replaced, since vfs1 will be deleted
soon anyway.

The following structs now use the new tool, with leak check enabled:
devpts:rootInode
fuse:inode
kernfs:Dentry
kernfs:dir
kernfs:readonlyDir
kernfs:StaticDirectory
proc:fdDirInode
proc:fdInfoDirInode
proc:subtasksInode
proc:taskInode
proc:tasksInode
vfs:FileDescription
vfs:MountNamespace
vfs:Filesystem
sys:dir
kernel:FSContext
kernel:ProcessGroup
kernel:Session
shm:Shm
mm:aioMappable
mm:SpecialMappable
transport:queue

And the following use the template, but because they currently are not leak
checked, a TODO is left instead of enabling leak check in this patch:
kernel:FDTable
tun:tunEndpoint

Updates #1486.

PiperOrigin-RevId: 328460377

2 files changed, 14 insertions, 5 deletions

diff --git a/pkg/refs_vfs2/BUILD b/pkg/refs_vfs2/BUILD
index 7b3e10683..577b827a5 100644
--- a/pkg/refs_vfs2/BUILD
+++ b/pkg/refs_vfs2/BUILD
@@ -11,7 +11,7 @@ go_template(
     types = [
         "T",
     ],
-    visibility = ["//pkg/sentry:internal"],
+    visibility = ["//:sandbox"],
     deps = [
         "//pkg/log",
         "//pkg/refs",
diff --git a/pkg/refs_vfs2/refs_template.go b/pkg/refs_vfs2/refs_template.go
index 99c43c065..d9b552896 100644
--- a/pkg/refs_vfs2/refs_template.go
+++ b/pkg/refs_vfs2/refs_template.go
@@ -12,11 +12,15 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Package refs_template defines a template that can be used by reference counted
-// objects.
+// 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.
 package refs_template
 
 import (
+	"fmt"
 	"runtime"
 	"sync/atomic"
 
@@ -38,6 +42,11 @@ var ownerType *T
 // 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 Refs struct {
 	// refCount is composed of two fields:
@@ -82,7 +91,7 @@ func (r *Refs) ReadRefs() int64 {
 //go:nosplit
 func (r *Refs) 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, ownerType))
 	}
 }
 
@@ -122,7 +131,7 @@ func (r *Refs) TryIncRef() bool {
 func (r *Refs) 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, ownerType))
 
 	case v == -1:
 		// Call the destructor.