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

4 files changed, 91 insertions, 26 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/BUILD b/pkg/sentry/fsimpl/kernfs/BUILD
index 3835557fe..637dca70c 100644
--- a/pkg/sentry/fsimpl/kernfs/BUILD
+++ b/pkg/sentry/fsimpl/kernfs/BUILD
@@ -26,9 +26,54 @@ go_template_instance(
     },
 )
 
+go_template_instance(
+    name = "dentry_refs",
+    out = "dentry_refs.go",
+    package = "kernfs",
+    prefix = "Dentry",
+    template = "//pkg/refs_vfs2:refs_template",
+    types = {
+        "T": "Dentry",
+    },
+)
+
+go_template_instance(
+    name = "static_directory_refs",
+    out = "static_directory_refs.go",
+    package = "kernfs",
+    prefix = "StaticDirectory",
+    template = "//pkg/refs_vfs2:refs_template",
+    types = {
+        "T": "StaticDirectory",
+    },
+)
+
+go_template_instance(
+    name = "dir_refs",
+    out = "dir_refs.go",
+    package = "kernfs_test",
+    prefix = "dir",
+    template = "//pkg/refs_vfs2:refs_template",
+    types = {
+        "T": "dir",
+    },
+)
+
+go_template_instance(
+    name = "readonly_dir_refs",
+    out = "readonly_dir_refs.go",
+    package = "kernfs_test",
+    prefix = "readonlyDir",
+    template = "//pkg/refs_vfs2:refs_template",
+    types = {
+        "T": "readonlyDir",
+    },
+)
+
 go_library(
     name = "kernfs",
     srcs = [
+        "dentry_refs.go",
         "dynamic_bytes_file.go",
         "fd_impl_util.go",
         "filesystem.go",
@@ -36,6 +81,7 @@ go_library(
         "inode_impl_util.go",
         "kernfs.go",
         "slot_list.go",
+        "static_directory_refs.go",
         "symlink.go",
     ],
     visibility = ["//pkg/sentry:internal"],
@@ -59,11 +105,17 @@ go_library(
 go_test(
     name = "kernfs_test",
     size = "small",
-    srcs = ["kernfs_test.go"],
+    srcs = [
+        "dir_refs.go",
+        "kernfs_test.go",
+        "readonly_dir_refs.go",
+    ],
     deps = [
         ":kernfs",
         "//pkg/abi/linux",
         "//pkg/context",
+        "//pkg/log",
+        "//pkg/refs",
         "//pkg/sentry/contexttest",
         "//pkg/sentry/fsimpl/testutil",
         "//pkg/sentry/kernel/auth",
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index 885856868..f442a5606 100644
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -20,7 +20,6 @@ import (
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
@@ -344,8 +343,6 @@ type OrderedChildrenOptions struct {
 //
 // Must be initialize with Init before first use.
 type OrderedChildren struct {
-	refs.AtomicRefCount
-
 	// Can children be modified by user syscalls? It set to false, interface
 	// methods that would modify the children return EPERM. Immutable.
 	writable bool
@@ -361,14 +358,14 @@ func (o *OrderedChildren) Init(opts OrderedChildrenOptions) {
 	o.set = make(map[string]*slot)
 }
 
-// DecRef implements Inode.DecRef.
-func (o *OrderedChildren) DecRef(ctx context.Context) {
-	o.AtomicRefCount.DecRefWithDestructor(ctx, func(context.Context) {
-		o.mu.Lock()
-		defer o.mu.Unlock()
-		o.order.Reset()
-		o.set = nil
-	})
+// Destroy clears the children stored in o. It should be called by structs
+// embedding OrderedChildren upon destruction, i.e. when their reference count
+// reaches zero.
+func (o *OrderedChildren) Destroy() {
+	o.mu.Lock()
+	defer o.mu.Unlock()
+	o.order.Reset()
+	o.set = nil
 }
 
 // Populate inserts children into this OrderedChildren, and d's dentry
@@ -549,6 +546,7 @@ func (InodeSymlink) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.D
 //
 // +stateify savable
 type StaticDirectory struct {
+	StaticDirectoryRefs
 	InodeNotSymlink
 	InodeDirectoryNoNewChildren
 	InodeAttrs
@@ -594,11 +592,16 @@ func (s *StaticDirectory) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd
 	return fd.VFSFileDescription(), nil
 }
 
-// SetStat implements Inode.SetStat not allowing inode attributes to be changed.
+// SetStat implements kernfs.Inode.SetStat not allowing inode attributes to be changed.
 func (*StaticDirectory) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
 	return syserror.EPERM
 }
 
+// DecRef implements kernfs.Inode.
+func (s *StaticDirectory) DecRef(context.Context) {
+	s.StaticDirectoryRefs.DecRef(s.Destroy)
+}
+
 // AlwaysValid partially implements kernfs.inodeDynamicLookup.
 type AlwaysValid struct{}
 
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index 51dbc050c..ca3685800 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -57,7 +57,6 @@ import (
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
@@ -161,9 +160,9 @@ const (
 //
 // Must be initialized by Init prior to first use.
 type Dentry struct {
-	vfsd vfs.Dentry
+	DentryRefs
 
-	refs.AtomicRefCount
+	vfsd vfs.Dentry
 
 	// flags caches useful information about the dentry from the inode. See the
 	// dflags* consts above. Must be accessed by atomic ops.
@@ -194,6 +193,7 @@ func (d *Dentry) Init(inode Inode) {
 	if ftype == linux.ModeSymlink {
 		d.flags |= dflagsIsSymlink
 	}
+	d.EnableLeakCheck()
 }
 
 // VFSDentry returns the generic vfs dentry for this kernfs dentry.
@@ -213,16 +213,14 @@ func (d *Dentry) isSymlink() bool {
 
 // DecRef implements vfs.DentryImpl.DecRef.
 func (d *Dentry) DecRef(ctx context.Context) {
-	d.AtomicRefCount.DecRefWithDestructor(ctx, d.destroy)
-}
-
-// Precondition: Dentry must be removed from VFS' dentry cache.
-func (d *Dentry) destroy(ctx context.Context) {
-	d.inode.DecRef(ctx) // IncRef from Init.
-	d.inode = nil
-	if d.parent != nil {
-		d.parent.DecRef(ctx) // IncRef from Dentry.InsertChild.
-	}
+	// Before the destructor is called, Dentry must be removed from VFS' dentry cache.
+	d.DentryRefs.DecRef(func() {
+		d.inode.DecRef(ctx) // IncRef from Init.
+		d.inode = nil
+		if d.parent != nil {
+			d.parent.DecRef(ctx) // IncRef from Dentry.InsertChild.
+		}
+	})
 }
 
 // InotifyWithParent implements vfs.DentryImpl.InotifyWithParent.
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs_test.go b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
index e5c28c0e4..e376d1736 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs_test.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
@@ -96,6 +96,7 @@ func (*attrs) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.S
 }
 
 type readonlyDir struct {
+	readonlyDirRefs
 	attrs
 	kernfs.InodeNotSymlink
 	kernfs.InodeNoDynamicLookup
@@ -111,6 +112,7 @@ func (fs *filesystem) newReadonlyDir(creds *auth.Credentials, mode linux.FileMod
 	dir := &readonlyDir{}
 	dir.attrs.Init(creds, 0 /* devMajor */, 0 /* devMinor */, fs.NextIno(), linux.ModeDirectory|mode)
 	dir.OrderedChildren.Init(kernfs.OrderedChildrenOptions{})
+	dir.EnableLeakCheck()
 	dir.dentry.Init(dir)
 
 	dir.IncLinks(dir.OrderedChildren.Populate(&dir.dentry, contents))
@@ -128,7 +130,12 @@ func (d *readonlyDir) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs
 	return fd.VFSFileDescription(), nil
 }
 
+func (d *readonlyDir) DecRef(context.Context) {
+	d.readonlyDirRefs.DecRef(d.Destroy)
+}
+
 type dir struct {
+	dirRefs
 	attrs
 	kernfs.InodeNotSymlink
 	kernfs.InodeNoDynamicLookup
@@ -145,6 +152,7 @@ func (fs *filesystem) newDir(creds *auth.Credentials, mode linux.FileMode, conte
 	dir.fs = fs
 	dir.attrs.Init(creds, 0 /* devMajor */, 0 /* devMinor */, fs.NextIno(), linux.ModeDirectory|mode)
 	dir.OrderedChildren.Init(kernfs.OrderedChildrenOptions{Writable: true})
+	dir.EnableLeakCheck()
 	dir.dentry.Init(dir)
 
 	dir.IncLinks(dir.OrderedChildren.Populate(&dir.dentry, contents))
@@ -162,6 +170,10 @@ func (d *dir) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry,
 	return fd.VFSFileDescription(), nil
 }
 
+func (d *dir) DecRef(context.Context) {
+	d.dirRefs.DecRef(d.Destroy)
+}
+
 func (d *dir) NewDir(ctx context.Context, name string, opts vfs.MkdirOptions) (*vfs.Dentry, error) {
 	creds := auth.CredentialsFromContext(ctx)
 	dir := d.fs.newDir(creds, opts.Mode, nil)