Merge release-20200622.1-333-gb44408b40 (automated)

3 files changed, 21 insertions, 142 deletions

diff --git a/pkg/sentry/fsimpl/tmpfs/inode_refs.go b/pkg/sentry/fsimpl/tmpfs/inode_refs.go
deleted file mode 100644
index 3d3f6ff11..000000000
--- a/pkg/sentry/fsimpl/tmpfs/inode_refs.go
+++ /dev/null
@@ -1,112 +0,0 @@
-package tmpfs
-
-import (
-	"sync/atomic"
-
-	"gvisor.dev/gvisor/pkg/log"
-	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
-	"runtime"
-)
-
-// ownerType is used to customize logging. Note that we use a pointer to T so
-// that we do not copy the entire object when passed as a format parameter.
-var inodeownerType *inode
-
-// 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 inodeRefs struct {
-	// refCount is composed of two fields:
-	//
-	//	[32-bit speculative references]:[32-bit real references]
-	//
-	// Speculative references are used for TryIncRef, to avoid a CompareAndSwap
-	// loop. See IncRef, DecRef and TryIncRef for details of how these fields are
-	// used.
-	refCount int64
-}
-
-func (r *inodeRefs) finalize() {
-	var note string
-	switch refs_vfs1.GetLeakMode() {
-	case refs_vfs1.NoLeakChecking:
-		return
-	case refs_vfs1.UninitializedLeakChecking:
-		note = "(Leak checker uninitialized): "
-	}
-	if n := r.ReadRefs(); n != 0 {
-		log.Warningf("%sAtomicRefCount %p owned by %T garbage collected with ref count of %d (want 0)", note, r, inodeownerType, n)
-	}
-}
-
-// EnableLeakCheck checks for reference leaks when Refs gets garbage collected.
-func (r *inodeRefs) EnableLeakCheck() {
-	if refs_vfs1.GetLeakMode() != refs_vfs1.NoLeakChecking {
-		runtime.SetFinalizer(r, (*inodeRefs).finalize)
-	}
-}
-
-// ReadRefs returns the current number of references. The returned count is
-// inherently racy and is unsafe to use without external synchronization.
-func (r *inodeRefs) ReadRefs() int64 {
-
-	return atomic.LoadInt64(&r.refCount) + 1
-}
-
-// IncRef implements refs.RefCounter.IncRef.
-//
-//go:nosplit
-func (r *inodeRefs) IncRef() {
-	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
-		panic("Incrementing non-positive ref count")
-	}
-}
-
-// TryIncRef implements refs.RefCounter.TryIncRef.
-//
-// To do this safely without a loop, a speculative reference is first acquired
-// on the object. This allows multiple concurrent TryIncRef calls to distinguish
-// other TryIncRef calls from genuine references held.
-//
-//go:nosplit
-func (r *inodeRefs) TryIncRef() bool {
-	const speculativeRef = 1 << 32
-	v := atomic.AddInt64(&r.refCount, speculativeRef)
-	if int32(v) < 0 {
-
-		atomic.AddInt64(&r.refCount, -speculativeRef)
-		return false
-	}
-
-	atomic.AddInt64(&r.refCount, -speculativeRef+1)
-	return true
-}
-
-// DecRef implements refs.RefCounter.DecRef.
-//
-// Note that speculative references are counted here. Since they were added
-// prior to real references reaching zero, they will successfully convert to
-// real references. In other words, we see speculative references only in the
-// following case:
-//
-//	A: TryIncRef [speculative increase => sees non-negative references]
-//	B: DecRef [real decrease]
-//	A: TryIncRef [transform speculative to real]
-//
-//go:nosplit
-func (r *inodeRefs) DecRef(destroy func()) {
-	switch v := atomic.AddInt64(&r.refCount, -1); {
-	case v < -1:
-		panic("Decrementing non-positive ref count")
-
-	case v == -1:
-
-		if destroy != nil {
-			destroy()
-		}
-	}
-}
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index 5640380dc..68e615e8b 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
@@ -285,10 +285,13 @@ type inode struct {
 	// fs is the owning filesystem. fs is immutable.
 	fs *filesystem
 
+	// refs is a reference count. refs is accessed using atomic memory
+	// operations.
+	//
 	// A reference is held on all inodes as long as they are reachable in the
 	// filesystem tree, i.e. nlink is nonzero. This reference is dropped when
 	// nlink reaches 0.
-	refs inodeRefs
+	refs int64
 
 	// xattrs implements extended attributes.
 	//
@@ -324,6 +327,7 @@ func (i *inode) init(impl interface{}, fs *filesystem, kuid auth.KUID, kgid auth
 		panic("file type is required in FileMode")
 	}
 	i.fs = fs
+	i.refs = 1
 	i.mode = uint32(mode)
 	i.uid = uint32(kuid)
 	i.gid = uint32(kgid)
@@ -335,7 +339,6 @@ func (i *inode) init(impl interface{}, fs *filesystem, kuid auth.KUID, kgid auth
 	i.mtime = now
 	// i.nlink initialized by caller
 	i.impl = impl
-	i.refs.EnableLeakCheck()
 }
 
 // incLinksLocked increments i's link count.
@@ -366,15 +369,25 @@ func (i *inode) decLinksLocked(ctx context.Context) {
 }
 
 func (i *inode) incRef() {
-	i.refs.IncRef()
+	if atomic.AddInt64(&i.refs, 1) <= 1 {
+		panic("tmpfs.inode.incRef() called without holding a reference")
+	}
 }
 
 func (i *inode) tryIncRef() bool {
-	return i.refs.TryIncRef()
+	for {
+		refs := atomic.LoadInt64(&i.refs)
+		if refs == 0 {
+			return false
+		}
+		if atomic.CompareAndSwapInt64(&i.refs, refs, refs+1) {
+			return true
+		}
+	}
 }
 
 func (i *inode) decRef(ctx context.Context) {
-	i.refs.DecRef(func() {
+	if refs := atomic.AddInt64(&i.refs, -1); refs == 0 {
 		i.watches.HandleDeletion(ctx)
 		if regFile, ok := i.impl.(*regularFile); ok {
 			// Release memory used by regFile to store data. Since regFile is
@@ -382,7 +395,9 @@ func (i *inode) decRef(ctx context.Context) {
 			// metadata.
 			regFile.data.DropAll(regFile.memFile)
 		}
-	})
+	} else if refs < 0 {
+		panic("tmpfs.inode.decRef() called without holding a reference")
+	}
 }
 
 func (i *inode) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes) error {
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go b/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
index d88136656..1b617bd35 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
@@ -58,31 +58,7 @@ func (x *dentryEntry) StateLoad(m state.Source) {
 	m.Load(1, &x.prev)
 }
 
-func (x *inodeRefs) StateTypeName() string {
-	return "pkg/sentry/fsimpl/tmpfs.inodeRefs"
-}
-
-func (x *inodeRefs) StateFields() []string {
-	return []string{
-		"refCount",
-	}
-}
-
-func (x *inodeRefs) beforeSave() {}
-
-func (x *inodeRefs) StateSave(m state.Sink) {
-	x.beforeSave()
-	m.Save(0, &x.refCount)
-}
-
-func (x *inodeRefs) afterLoad() {}
-
-func (x *inodeRefs) StateLoad(m state.Source) {
-	m.Load(0, &x.refCount)
-}
-
 func init() {
 	state.Register((*dentryList)(nil))
 	state.Register((*dentryEntry)(nil))
-	state.Register((*inodeRefs)(nil))
 }