Merge release-20200818.0-56-gdf3c105f4 (automated)

3 files changed, 157 insertions, 1 deletions

diff --git a/pkg/sentry/fsimpl/sys/dir_refs.go b/pkg/sentry/fsimpl/sys/dir_refs.go
new file mode 100644
index 000000000..89609b198
--- /dev/null
+++ b/pkg/sentry/fsimpl/sys/dir_refs.go
@@ -0,0 +1,118 @@
+package sys
+
+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 dirownerType *dir
+
+// 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 dirRefs 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 *dirRefs) 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, dirownerType, n)
+	}
+}
+
+// EnableLeakCheck checks for reference leaks when Refs gets garbage collected.
+func (r *dirRefs) EnableLeakCheck() {
+	if refs_vfs1.GetLeakMode() != refs_vfs1.NoLeakChecking {
+		runtime.SetFinalizer(r, (*dirRefs).finalize)
+	}
+}
+
+// ReadRefs returns the current number of references. The returned count is
+// inherently racy and is unsafe to use without external synchronization.
+func (r *dirRefs) ReadRefs() int64 {
+
+	return atomic.LoadInt64(&r.refCount) + 1
+}
+
+// IncRef implements refs.RefCounter.IncRef.
+//
+//go:nosplit
+func (r *dirRefs) IncRef() {
+	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
+		panic(fmt.Sprintf("Incrementing non-positive ref count %p owned by %T", r, dirownerType))
+	}
+}
+
+// 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 *dirRefs) 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 *dirRefs) 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, dirownerType))
+
+	case v == -1:
+
+		if destroy != nil {
+			destroy()
+		}
+	}
+}
diff --git a/pkg/sentry/fsimpl/sys/sys.go b/pkg/sentry/fsimpl/sys/sys.go
index 1f042d9f7..ea30a4ec2 100644
--- a/pkg/sentry/fsimpl/sys/sys.go
+++ b/pkg/sentry/fsimpl/sys/sys.go
@@ -118,6 +118,7 @@ func (fs *filesystem) Release(ctx context.Context) {
 
 // dir implements kernfs.Inode.
 type dir struct {
+	dirRefs
 	kernfs.InodeAttrs
 	kernfs.InodeNoDynamicLookup
 	kernfs.InodeNotSymlink
@@ -133,6 +134,7 @@ func (fs *filesystem) newDir(creds *auth.Credentials, mode linux.FileMode, conte
 	d := &dir{}
 	d.InodeAttrs.Init(creds, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), linux.ModeDirectory|0755)
 	d.OrderedChildren.Init(kernfs.OrderedChildrenOptions{})
+	d.EnableLeakCheck()
 	d.dentry.Init(d)
 
 	d.IncLinks(d.OrderedChildren.Populate(&d.dentry, contents))
@@ -140,7 +142,7 @@ func (fs *filesystem) newDir(creds *auth.Credentials, mode linux.FileMode, conte
 	return &d.dentry
 }
 
-// SetStat implements Inode.SetStat not allowing inode attributes to be changed.
+// SetStat implements kernfs.Inode.SetStat not allowing inode attributes to be changed.
 func (*dir) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
 	return syserror.EPERM
 }
@@ -156,6 +158,11 @@ func (d *dir) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry,
 	return fd.VFSFileDescription(), nil
 }
 
+// DecRef implements kernfs.Inode.DecRef.
+func (d *dir) DecRef(context.Context) {
+	d.dirRefs.DecRef(d.Destroy)
+}
+
 // cpuFile implements kernfs.Inode.
 type cpuFile struct {
 	kernfs.DynamicBytesFile
diff --git a/pkg/sentry/fsimpl/sys/sys_state_autogen.go b/pkg/sentry/fsimpl/sys/sys_state_autogen.go
index 8866ddff9..347a46318 100644
--- a/pkg/sentry/fsimpl/sys/sys_state_autogen.go
+++ b/pkg/sentry/fsimpl/sys/sys_state_autogen.go
@@ -1,3 +1,34 @@
 // automatically generated by stateify.
 
 package sys
+
+import (
+	"gvisor.dev/gvisor/pkg/state"
+)
+
+func (x *dirRefs) StateTypeName() string {
+	return "pkg/sentry/fsimpl/sys.dirRefs"
+}
+
+func (x *dirRefs) StateFields() []string {
+	return []string{
+		"refCount",
+	}
+}
+
+func (x *dirRefs) beforeSave() {}
+
+func (x *dirRefs) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.refCount)
+}
+
+func (x *dirRefs) afterLoad() {}
+
+func (x *dirRefs) StateLoad(m state.Source) {
+	m.Load(0, &x.refCount)
+}
+
+func init() {
+	state.Register((*dirRefs)(nil))
+}