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, 21 insertions, 11 deletions

diff --git a/pkg/sentry/kernel/shm/BUILD b/pkg/sentry/kernel/shm/BUILD
index c211fc8d0..b7e4b480d 100644
--- a/pkg/sentry/kernel/shm/BUILD
+++ b/pkg/sentry/kernel/shm/BUILD
@@ -1,12 +1,25 @@
 load("//tools:defs.bzl", "go_library")
+load("//tools/go_generics:defs.bzl", "go_template_instance")
 
 package(licenses = ["notice"])
 
+go_template_instance(
+    name = "shm_refs",
+    out = "shm_refs.go",
+    package = "shm",
+    prefix = "Shm",
+    template = "//pkg/refs_vfs2:refs_template",
+    types = {
+        "T": "Shm",
+    },
+)
+
 go_library(
     name = "shm",
     srcs = [
         "device.go",
         "shm.go",
+        "shm_refs.go",
     ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
diff --git a/pkg/sentry/kernel/shm/shm.go b/pkg/sentry/kernel/shm/shm.go
index 13ec7afe0..00c03585e 100644
--- a/pkg/sentry/kernel/shm/shm.go
+++ b/pkg/sentry/kernel/shm/shm.go
@@ -39,7 +39,6 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/log"
-	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
@@ -252,7 +251,7 @@ func (r *Registry) newShm(ctx context.Context, pid int32, key Key, creator fs.Fi
 		creatorPID:    pid,
 		changeTime:    ktime.NowFromContext(ctx),
 	}
-	shm.EnableLeakCheck("kernel.Shm")
+	shm.EnableLeakCheck()
 
 	// Find the next available ID.
 	for id := r.lastIDUsed + 1; id != r.lastIDUsed; id++ {
@@ -337,14 +336,14 @@ func (r *Registry) remove(s *Shm) {
 //
 // +stateify savable
 type Shm struct {
-	// AtomicRefCount tracks the number of references to this segment.
+	// ShmRefs tracks the number of references to this segment.
 	//
 	// A segment holds a reference to itself until it is marked for
 	// destruction.
 	//
 	// In addition to direct users, the MemoryManager will hold references
 	// via MappingIdentity.
-	refs.AtomicRefCount
+	ShmRefs
 
 	mfp pgalloc.MemoryFileProvider
 
@@ -428,11 +427,14 @@ func (s *Shm) InodeID() uint64 {
 	return uint64(s.ID)
 }
 
-// DecRef overrides refs.RefCount.DecRef with a destructor.
+// DecRef drops a reference on s.
 //
 // Precondition: Caller must not hold s.mu.
 func (s *Shm) DecRef(ctx context.Context) {
-	s.DecRefWithDestructor(ctx, s.destroy)
+	s.ShmRefs.DecRef(func() {
+		s.mfp.MemoryFile().DecRef(s.fr)
+		s.registry.remove(s)
+	})
 }
 
 // Msync implements memmap.MappingIdentity.Msync. Msync is a no-op for shm
@@ -642,11 +644,6 @@ func (s *Shm) Set(ctx context.Context, ds *linux.ShmidDS) error {
 	return nil
 }
 
-func (s *Shm) destroy(context.Context) {
-	s.mfp.MemoryFile().DecRef(s.fr)
-	s.registry.remove(s)
-}
-
 // MarkDestroyed marks a segment for destruction. The segment is actually
 // destroyed once it has no references. MarkDestroyed may be called multiple
 // times, and is safe to call after a segment has already been destroyed. See