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

1 files changed, 47 insertions, 42 deletions

diff --git a/pkg/sentry/kernel/fs_context.go b/pkg/sentry/kernel/fs_context.go
index 8f2d36d5a..d46d1e1c1 100644
--- a/pkg/sentry/kernel/fs_context.go
+++ b/pkg/sentry/kernel/fs_context.go
@@ -18,7 +18,6 @@ import (
 	"fmt"
 
 	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
@@ -30,7 +29,7 @@ import (
 //
 // +stateify savable
 type FSContext struct {
-	refs.AtomicRefCount
+	FSContextRefs
 
 	// mu protects below.
 	mu sync.Mutex `state:"nosave"`
@@ -64,7 +63,7 @@ func newFSContext(root, cwd *fs.Dirent, umask uint) *FSContext {
 		cwd:   cwd,
 		umask: umask,
 	}
-	f.EnableLeakCheck("kernel.FSContext")
+	f.EnableLeakCheck()
 	return &f
 }
 
@@ -77,54 +76,56 @@ func NewFSContextVFS2(root, cwd vfs.VirtualDentry, umask uint) *FSContext {
 		cwdVFS2:  cwd,
 		umask:    umask,
 	}
-	f.EnableLeakCheck("kernel.FSContext")
+	f.EnableLeakCheck()
 	return &f
 }
 
-// destroy is the destructor for an FSContext.
+// DecRef implements RefCounter.DecRef.
 //
-// This will call DecRef on both root and cwd Dirents.  If either call to
-// DecRef returns an error, then it will be propagated.  If both calls to
-// DecRef return an error, then the one from root.DecRef will be propagated.
+// When f reaches zero references, DecRef will be called on both root and cwd
+// Dirents.
 //
 // Note that there may still be calls to WorkingDirectory() or RootDirectory()
 // (that return nil).  This is because valid references may still be held via
 // proc files or other mechanisms.
-func (f *FSContext) destroy(ctx context.Context) {
-	// Hold f.mu so that we don't race with RootDirectory() and
-	// WorkingDirectory().
-	f.mu.Lock()
-	defer f.mu.Unlock()
-
-	if VFS2Enabled {
-		f.rootVFS2.DecRef(ctx)
-		f.rootVFS2 = vfs.VirtualDentry{}
-		f.cwdVFS2.DecRef(ctx)
-		f.cwdVFS2 = vfs.VirtualDentry{}
-	} else {
-		f.root.DecRef(ctx)
-		f.root = nil
-		f.cwd.DecRef(ctx)
-		f.cwd = nil
-	}
-}
-
-// DecRef implements RefCounter.DecRef with destructor f.destroy.
 func (f *FSContext) DecRef(ctx context.Context) {
-	f.DecRefWithDestructor(ctx, f.destroy)
+	f.FSContextRefs.DecRef(func() {
+		// Hold f.mu so that we don't race with RootDirectory() and
+		// WorkingDirectory().
+		f.mu.Lock()
+		defer f.mu.Unlock()
+
+		if VFS2Enabled {
+			f.rootVFS2.DecRef(ctx)
+			f.rootVFS2 = vfs.VirtualDentry{}
+			f.cwdVFS2.DecRef(ctx)
+			f.cwdVFS2 = vfs.VirtualDentry{}
+		} else {
+			f.root.DecRef(ctx)
+			f.root = nil
+			f.cwd.DecRef(ctx)
+			f.cwd = nil
+		}
+	})
 }
 
 // Fork forks this FSContext.
 //
-// This is not a valid call after destroy.
+// This is not a valid call after f is destroyed.
 func (f *FSContext) Fork() *FSContext {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 
 	if VFS2Enabled {
+		if !f.cwdVFS2.Ok() {
+			panic("FSContext.Fork() called after destroy")
+		}
 		f.cwdVFS2.IncRef()
 		f.rootVFS2.IncRef()
 	} else {
+		if f.cwd == nil {
+			panic("FSContext.Fork() called after destroy")
+		}
 		f.cwd.IncRef()
 		f.root.IncRef()
 	}
@@ -140,8 +141,8 @@ func (f *FSContext) Fork() *FSContext {
 
 // WorkingDirectory returns the current working directory.
 //
-// This will return nil if called after destroy(), otherwise it will return a
-// Dirent with a reference taken.
+// This will return nil if called after f is destroyed, otherwise it will return
+// a Dirent with a reference taken.
 func (f *FSContext) WorkingDirectory() *fs.Dirent {
 	f.mu.Lock()
 	defer f.mu.Unlock()
@@ -152,8 +153,8 @@ func (f *FSContext) WorkingDirectory() *fs.Dirent {
 
 // WorkingDirectoryVFS2 returns the current working directory.
 //
-// This will return nil if called after destroy(), otherwise it will return a
-// Dirent with a reference taken.
+// This will return nil if called after f is destroyed, otherwise it will return
+// a Dirent with a reference taken.
 func (f *FSContext) WorkingDirectoryVFS2() vfs.VirtualDentry {
 	f.mu.Lock()
 	defer f.mu.Unlock()
@@ -165,7 +166,7 @@ func (f *FSContext) WorkingDirectoryVFS2() vfs.VirtualDentry {
 // SetWorkingDirectory sets the current working directory.
 // This will take an extra reference on the Dirent.
 //
-// This is not a valid call after destroy.
+// This is not a valid call after f is destroyed.
 func (f *FSContext) SetWorkingDirectory(ctx context.Context, d *fs.Dirent) {
 	if d == nil {
 		panic("FSContext.SetWorkingDirectory called with nil dirent")
@@ -187,11 +188,15 @@ func (f *FSContext) SetWorkingDirectory(ctx context.Context, d *fs.Dirent) {
 // SetWorkingDirectoryVFS2 sets the current working directory.
 // This will take an extra reference on the VirtualDentry.
 //
-// This is not a valid call after destroy.
+// This is not a valid call after f is destroyed.
 func (f *FSContext) SetWorkingDirectoryVFS2(ctx context.Context, d vfs.VirtualDentry) {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 
+	if !f.cwdVFS2.Ok() {
+		panic(fmt.Sprintf("FSContext.SetWorkingDirectoryVFS2(%v)) called after destroy", d))
+	}
+
 	old := f.cwdVFS2
 	f.cwdVFS2 = d
 	d.IncRef()
@@ -200,8 +205,8 @@ func (f *FSContext) SetWorkingDirectoryVFS2(ctx context.Context, d vfs.VirtualDe
 
 // RootDirectory returns the current filesystem root.
 //
-// This will return nil if called after destroy(), otherwise it will return a
-// Dirent with a reference taken.
+// This will return nil if called after f is destroyed, otherwise it will return
+// a Dirent with a reference taken.
 func (f *FSContext) RootDirectory() *fs.Dirent {
 	f.mu.Lock()
 	defer f.mu.Unlock()
@@ -213,8 +218,8 @@ func (f *FSContext) RootDirectory() *fs.Dirent {
 
 // RootDirectoryVFS2 returns the current filesystem root.
 //
-// This will return nil if called after destroy(), otherwise it will return a
-// Dirent with a reference taken.
+// This will return nil if called after f is destroyed, otherwise it will return
+// a Dirent with a reference taken.
 func (f *FSContext) RootDirectoryVFS2() vfs.VirtualDentry {
 	f.mu.Lock()
 	defer f.mu.Unlock()
@@ -226,7 +231,7 @@ func (f *FSContext) RootDirectoryVFS2() vfs.VirtualDentry {
 // SetRootDirectory sets the root directory.
 // This will take an extra reference on the Dirent.
 //
-// This is not a valid call after free.
+// This is not a valid call after f is destroyed.
 func (f *FSContext) SetRootDirectory(ctx context.Context, d *fs.Dirent) {
 	if d == nil {
 		panic("FSContext.SetRootDirectory called with nil dirent")
@@ -247,7 +252,7 @@ func (f *FSContext) SetRootDirectory(ctx context.Context, d *fs.Dirent) {
 
 // SetRootDirectoryVFS2 sets the root directory. It takes a reference on vd.
 //
-// This is not a valid call after free.
+// This is not a valid call after f is destroyed.
 func (f *FSContext) SetRootDirectoryVFS2(ctx context.Context, vd vfs.VirtualDentry) {
 	if !vd.Ok() {
 		panic("FSContext.SetRootDirectoryVFS2 called with zero-value VirtualDentry")