Merge release-20200818.0-56-gdf3c105f4 (automated)

5 files changed, 327 insertions, 39 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/dentry_refs.go b/pkg/sentry/fsimpl/kernfs/dentry_refs.go
new file mode 100644
index 000000000..79863b3bc
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/dentry_refs.go
@@ -0,0 +1,118 @@
+package kernfs
+
+import (
+	"fmt"
+	"runtime"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/log"
+	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
+)
+
+// 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 DentryownerType *Dentry
+
+// 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.
+//
+// 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 DentryRefs 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 *DentryRefs) 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("%sRefs %p owned by %T garbage collected with ref count of %d (want 0)", note, r, DentryownerType, n)
+	}
+}
+
+// EnableLeakCheck checks for reference leaks when Refs gets garbage collected.
+func (r *DentryRefs) EnableLeakCheck() {
+	if refs_vfs1.GetLeakMode() != refs_vfs1.NoLeakChecking {
+		runtime.SetFinalizer(r, (*DentryRefs).finalize)
+	}
+}
+
+// ReadRefs returns the current number of references. The returned count is
+// inherently racy and is unsafe to use without external synchronization.
+func (r *DentryRefs) ReadRefs() int64 {
+
+	return atomic.LoadInt64(&r.refCount) + 1
+}
+
+// IncRef implements refs.RefCounter.IncRef.
+//
+//go:nosplit
+func (r *DentryRefs) IncRef() {
+	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
+		panic(fmt.Sprintf("Incrementing non-positive ref count %p owned by %T", r, DentryownerType))
+	}
+}
+
+// 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 *DentryRefs) 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 *DentryRefs) DecRef(destroy func()) {
+	switch v := atomic.AddInt64(&r.refCount, -1); {
+	case v < -1:
+		panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %T", r, DentryownerType))
+
+	case v == -1:
+
+		if destroy != nil {
+			destroy()
+		}
+	}
+}
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_state_autogen.go b/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go
index f396affb0..12aaf797f 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go
@@ -6,6 +6,29 @@ import (
 	"gvisor.dev/gvisor/pkg/state"
 )
 
+func (x *DentryRefs) StateTypeName() string {
+	return "pkg/sentry/fsimpl/kernfs.DentryRefs"
+}
+
+func (x *DentryRefs) StateFields() []string {
+	return []string{
+		"refCount",
+	}
+}
+
+func (x *DentryRefs) beforeSave() {}
+
+func (x *DentryRefs) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.refCount)
+}
+
+func (x *DentryRefs) afterLoad() {}
+
+func (x *DentryRefs) StateLoad(m state.Source) {
+	m.Load(0, &x.refCount)
+}
+
 func (x *DynamicBytesFile) StateTypeName() string {
 	return "pkg/sentry/fsimpl/kernfs.DynamicBytesFile"
 }
@@ -85,6 +108,7 @@ func (x *StaticDirectory) StateTypeName() string {
 
 func (x *StaticDirectory) StateFields() []string {
 	return []string{
+		"StaticDirectoryRefs",
 		"InodeNotSymlink",
 		"InodeDirectoryNoNewChildren",
 		"InodeAttrs",
@@ -99,25 +123,27 @@ func (x *StaticDirectory) beforeSave() {}
 
 func (x *StaticDirectory) StateSave(m state.Sink) {
 	x.beforeSave()
-	m.Save(0, &x.InodeNotSymlink)
-	m.Save(1, &x.InodeDirectoryNoNewChildren)
-	m.Save(2, &x.InodeAttrs)
-	m.Save(3, &x.InodeNoDynamicLookup)
-	m.Save(4, &x.OrderedChildren)
-	m.Save(5, &x.locks)
-	m.Save(6, &x.fdOpts)
+	m.Save(0, &x.StaticDirectoryRefs)
+	m.Save(1, &x.InodeNotSymlink)
+	m.Save(2, &x.InodeDirectoryNoNewChildren)
+	m.Save(3, &x.InodeAttrs)
+	m.Save(4, &x.InodeNoDynamicLookup)
+	m.Save(5, &x.OrderedChildren)
+	m.Save(6, &x.locks)
+	m.Save(7, &x.fdOpts)
 }
 
 func (x *StaticDirectory) afterLoad() {}
 
 func (x *StaticDirectory) StateLoad(m state.Source) {
-	m.Load(0, &x.InodeNotSymlink)
-	m.Load(1, &x.InodeDirectoryNoNewChildren)
-	m.Load(2, &x.InodeAttrs)
-	m.Load(3, &x.InodeNoDynamicLookup)
-	m.Load(4, &x.OrderedChildren)
-	m.Load(5, &x.locks)
-	m.Load(6, &x.fdOpts)
+	m.Load(0, &x.StaticDirectoryRefs)
+	m.Load(1, &x.InodeNotSymlink)
+	m.Load(2, &x.InodeDirectoryNoNewChildren)
+	m.Load(3, &x.InodeAttrs)
+	m.Load(4, &x.InodeNoDynamicLookup)
+	m.Load(5, &x.OrderedChildren)
+	m.Load(6, &x.locks)
+	m.Load(7, &x.fdOpts)
 }
 
 func (x *slotList) StateTypeName() string {
@@ -172,10 +198,35 @@ func (x *slotEntry) StateLoad(m state.Source) {
 	m.Load(1, &x.prev)
 }
 
+func (x *StaticDirectoryRefs) StateTypeName() string {
+	return "pkg/sentry/fsimpl/kernfs.StaticDirectoryRefs"
+}
+
+func (x *StaticDirectoryRefs) StateFields() []string {
+	return []string{
+		"refCount",
+	}
+}
+
+func (x *StaticDirectoryRefs) beforeSave() {}
+
+func (x *StaticDirectoryRefs) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.refCount)
+}
+
+func (x *StaticDirectoryRefs) afterLoad() {}
+
+func (x *StaticDirectoryRefs) StateLoad(m state.Source) {
+	m.Load(0, &x.refCount)
+}
+
 func init() {
+	state.Register((*DentryRefs)(nil))
 	state.Register((*DynamicBytesFile)(nil))
 	state.Register((*DynamicBytesFD)(nil))
 	state.Register((*StaticDirectory)(nil))
 	state.Register((*slotList)(nil))
 	state.Register((*slotEntry)(nil))
+	state.Register((*StaticDirectoryRefs)(nil))
 }
diff --git a/pkg/sentry/fsimpl/kernfs/static_directory_refs.go b/pkg/sentry/fsimpl/kernfs/static_directory_refs.go
new file mode 100644
index 000000000..478b04bdd
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/static_directory_refs.go
@@ -0,0 +1,118 @@
+package kernfs
+
+import (
+	"fmt"
+	"runtime"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/log"
+	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
+)
+
+// 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 StaticDirectoryownerType *StaticDirectory
+
+// 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.
+//
+// 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 StaticDirectoryRefs 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 *StaticDirectoryRefs) 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("%sRefs %p owned by %T garbage collected with ref count of %d (want 0)", note, r, StaticDirectoryownerType, n)
+	}
+}
+
+// EnableLeakCheck checks for reference leaks when Refs gets garbage collected.
+func (r *StaticDirectoryRefs) EnableLeakCheck() {
+	if refs_vfs1.GetLeakMode() != refs_vfs1.NoLeakChecking {
+		runtime.SetFinalizer(r, (*StaticDirectoryRefs).finalize)
+	}
+}
+
+// ReadRefs returns the current number of references. The returned count is
+// inherently racy and is unsafe to use without external synchronization.
+func (r *StaticDirectoryRefs) ReadRefs() int64 {
+
+	return atomic.LoadInt64(&r.refCount) + 1
+}
+
+// IncRef implements refs.RefCounter.IncRef.
+//
+//go:nosplit
+func (r *StaticDirectoryRefs) IncRef() {
+	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
+		panic(fmt.Sprintf("Incrementing non-positive ref count %p owned by %T", r, StaticDirectoryownerType))
+	}
+}
+
+// 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 *StaticDirectoryRefs) 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 *StaticDirectoryRefs) DecRef(destroy func()) {
+	switch v := atomic.AddInt64(&r.refCount, -1); {
+	case v < -1:
+		panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %T", r, StaticDirectoryownerType))
+
+	case v == -1:
+
+		if destroy != nil {
+			destroy()
+		}
+	}
+}