3 files changed, 287 insertions, 46 deletions
diff --git a/pkg/sentry/kernel/shm/BUILD b/pkg/sentry/kernel/shm/BUILD
deleted file mode 100644
index 1c3c0794f..000000000
--- a/pkg/sentry/kernel/shm/BUILD
+++ /dev/null
@@ -1,46 +0,0 @@
-load("//tools:defs.bzl", "go_library")
-load("//tools/go_generics:defs.bzl", "go_template_instance")
-
-package(licenses = ["notice"])
-
-go_template_instance(
-    name = "shm_refs",
-    out = "shm_refs.go",
-    consts = {
-        "enableLogging": "true",
-    },
-    package = "shm",
-    prefix = "Shm",
-    template = "//pkg/refsvfs2:refs_template",
-    types = {
-        "T": "Shm",
-    },
-)
-
-go_library(
-    name = "shm",
-    srcs = [
-        "device.go",
-        "shm.go",
-        "shm_refs.go",
-    ],
-    visibility = ["//pkg/sentry:internal"],
-    deps = [
-        "//pkg/abi/linux",
-        "//pkg/context",
-        "//pkg/hostarch",
-        "//pkg/log",
-        "//pkg/refs",
-        "//pkg/refsvfs2",
-        "//pkg/sentry/device",
-        "//pkg/sentry/fs",
-        "//pkg/sentry/kernel/auth",
-        "//pkg/sentry/kernel/time",
-        "//pkg/sentry/memmap",
-        "//pkg/sentry/pgalloc",
-        "//pkg/sentry/usage",
-        "//pkg/sync",
-        "//pkg/syserror",
-        "//pkg/usermem",
-    ],
-)
diff --git a/pkg/sentry/kernel/shm/shm_refs.go b/pkg/sentry/kernel/shm/shm_refs.go
new file mode 100644
index 000000000..f832c1a99
--- /dev/null
+++ b/pkg/sentry/kernel/shm/shm_refs.go
@@ -0,0 +1,140 @@
+package shm
+
+import (
+	"fmt"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/refsvfs2"
+)
+
+// enableLogging indicates whether reference-related events should be logged (with
+// stack traces). This is false by default and should only be set to true for
+// debugging purposes, as it can generate an extremely large amount of output
+// and drastically degrade performance.
+const ShmenableLogging = true
+
+// obj 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 Shmobj *Shm
+
+// Refs implements refs.RefCounter. It keeps a reference count using atomic
+// operations and calls the destructor when the count reaches zero.
+//
+// NOTE: Do not introduce additional fields to the Refs struct. It is used by
+// many filesystem objects, and we want to keep it as small as possible (i.e.,
+// the same size as using an int64 directly) to avoid taking up extra cache
+// space. In general, this template should not be extended at the cost of
+// performance. If it does not offer enough flexibility for a particular object
+// (example: b/187877947), we should implement the RefCounter/CheckedObject
+// interfaces manually.
+//
+// +stateify savable
+type ShmRefs 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
+}
+
+// InitRefs initializes r with one reference and, if enabled, activates leak
+// checking.
+func (r *ShmRefs) InitRefs() {
+	atomic.StoreInt64(&r.refCount, 1)
+	refsvfs2.Register(r)
+}
+
+// RefType implements refsvfs2.CheckedObject.RefType.
+func (r *ShmRefs) RefType() string {
+	return fmt.Sprintf("%T", Shmobj)[1:]
+}
+
+// LeakMessage implements refsvfs2.CheckedObject.LeakMessage.
+func (r *ShmRefs) LeakMessage() string {
+	return fmt.Sprintf("[%s %p] reference count of %d instead of 0", r.RefType(), r, r.ReadRefs())
+}
+
+// LogRefs implements refsvfs2.CheckedObject.LogRefs.
+func (r *ShmRefs) LogRefs() bool {
+	return ShmenableLogging
+}
+
+// ReadRefs returns the current number of references. The returned count is
+// inherently racy and is unsafe to use without external synchronization.
+func (r *ShmRefs) ReadRefs() int64 {
+	return atomic.LoadInt64(&r.refCount)
+}
+
+// IncRef implements refs.RefCounter.IncRef.
+//
+//go:nosplit
+func (r *ShmRefs) IncRef() {
+	v := atomic.AddInt64(&r.refCount, 1)
+	if ShmenableLogging {
+		refsvfs2.LogIncRef(r, v)
+	}
+	if v <= 1 {
+		panic(fmt.Sprintf("Incrementing non-positive count %p on %s", r, r.RefType()))
+	}
+}
+
+// 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 *ShmRefs) TryIncRef() bool {
+	const speculativeRef = 1 << 32
+	if v := atomic.AddInt64(&r.refCount, speculativeRef); int32(v) == 0 {
+
+		atomic.AddInt64(&r.refCount, -speculativeRef)
+		return false
+	}
+
+	v := atomic.AddInt64(&r.refCount, -speculativeRef+1)
+	if ShmenableLogging {
+		refsvfs2.LogTryIncRef(r, v)
+	}
+	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 *ShmRefs) DecRef(destroy func()) {
+	v := atomic.AddInt64(&r.refCount, -1)
+	if ShmenableLogging {
+		refsvfs2.LogDecRef(r, v)
+	}
+	switch {
+	case v < 0:
+		panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %s", r, r.RefType()))
+
+	case v == 0:
+		refsvfs2.Unregister(r)
+
+		if destroy != nil {
+			destroy()
+		}
+	}
+}
+
+func (r *ShmRefs) afterLoad() {
+	if r.ReadRefs() > 0 {
+		refsvfs2.Register(r)
+	}
+}
diff --git a/pkg/sentry/kernel/shm/shm_state_autogen.go b/pkg/sentry/kernel/shm/shm_state_autogen.go
new file mode 100644
index 000000000..30ceeaa03
--- /dev/null
+++ b/pkg/sentry/kernel/shm/shm_state_autogen.go
@@ -0,0 +1,147 @@
+// automatically generated by stateify.
+
+package shm
+
+import (
+	"gvisor.dev/gvisor/pkg/state"
+)
+
+func (r *Registry) StateTypeName() string {
+	return "pkg/sentry/kernel/shm.Registry"
+}
+
+func (r *Registry) StateFields() []string {
+	return []string{
+		"userNS",
+		"shms",
+		"keysToShms",
+		"totalPages",
+		"lastIDUsed",
+	}
+}
+
+func (r *Registry) beforeSave() {}
+
+// +checklocksignore
+func (r *Registry) StateSave(stateSinkObject state.Sink) {
+	r.beforeSave()
+	stateSinkObject.Save(0, &r.userNS)
+	stateSinkObject.Save(1, &r.shms)
+	stateSinkObject.Save(2, &r.keysToShms)
+	stateSinkObject.Save(3, &r.totalPages)
+	stateSinkObject.Save(4, &r.lastIDUsed)
+}
+
+func (r *Registry) afterLoad() {}
+
+// +checklocksignore
+func (r *Registry) StateLoad(stateSourceObject state.Source) {
+	stateSourceObject.Load(0, &r.userNS)
+	stateSourceObject.Load(1, &r.shms)
+	stateSourceObject.Load(2, &r.keysToShms)
+	stateSourceObject.Load(3, &r.totalPages)
+	stateSourceObject.Load(4, &r.lastIDUsed)
+}
+
+func (s *Shm) StateTypeName() string {
+	return "pkg/sentry/kernel/shm.Shm"
+}
+
+func (s *Shm) StateFields() []string {
+	return []string{
+		"ShmRefs",
+		"mfp",
+		"registry",
+		"ID",
+		"creator",
+		"size",
+		"effectiveSize",
+		"fr",
+		"key",
+		"perms",
+		"owner",
+		"attachTime",
+		"detachTime",
+		"changeTime",
+		"creatorPID",
+		"lastAttachDetachPID",
+		"pendingDestruction",
+	}
+}
+
+func (s *Shm) beforeSave() {}
+
+// +checklocksignore
+func (s *Shm) StateSave(stateSinkObject state.Sink) {
+	s.beforeSave()
+	stateSinkObject.Save(0, &s.ShmRefs)
+	stateSinkObject.Save(1, &s.mfp)
+	stateSinkObject.Save(2, &s.registry)
+	stateSinkObject.Save(3, &s.ID)
+	stateSinkObject.Save(4, &s.creator)
+	stateSinkObject.Save(5, &s.size)
+	stateSinkObject.Save(6, &s.effectiveSize)
+	stateSinkObject.Save(7, &s.fr)
+	stateSinkObject.Save(8, &s.key)
+	stateSinkObject.Save(9, &s.perms)
+	stateSinkObject.Save(10, &s.owner)
+	stateSinkObject.Save(11, &s.attachTime)
+	stateSinkObject.Save(12, &s.detachTime)
+	stateSinkObject.Save(13, &s.changeTime)
+	stateSinkObject.Save(14, &s.creatorPID)
+	stateSinkObject.Save(15, &s.lastAttachDetachPID)
+	stateSinkObject.Save(16, &s.pendingDestruction)
+}
+
+func (s *Shm) afterLoad() {}
+
+// +checklocksignore
+func (s *Shm) StateLoad(stateSourceObject state.Source) {
+	stateSourceObject.Load(0, &s.ShmRefs)
+	stateSourceObject.Load(1, &s.mfp)
+	stateSourceObject.Load(2, &s.registry)
+	stateSourceObject.Load(3, &s.ID)
+	stateSourceObject.Load(4, &s.creator)
+	stateSourceObject.Load(5, &s.size)
+	stateSourceObject.Load(6, &s.effectiveSize)
+	stateSourceObject.Load(7, &s.fr)
+	stateSourceObject.Load(8, &s.key)
+	stateSourceObject.Load(9, &s.perms)
+	stateSourceObject.Load(10, &s.owner)
+	stateSourceObject.Load(11, &s.attachTime)
+	stateSourceObject.Load(12, &s.detachTime)
+	stateSourceObject.Load(13, &s.changeTime)
+	stateSourceObject.Load(14, &s.creatorPID)
+	stateSourceObject.Load(15, &s.lastAttachDetachPID)
+	stateSourceObject.Load(16, &s.pendingDestruction)
+}
+
+func (r *ShmRefs) StateTypeName() string {
+	return "pkg/sentry/kernel/shm.ShmRefs"
+}
+
+func (r *ShmRefs) StateFields() []string {
+	return []string{
+		"refCount",
+	}
+}
+
+func (r *ShmRefs) beforeSave() {}
+
+// +checklocksignore
+func (r *ShmRefs) StateSave(stateSinkObject state.Sink) {
+	r.beforeSave()
+	stateSinkObject.Save(0, &r.refCount)
+}
+
+// +checklocksignore
+func (r *ShmRefs) StateLoad(stateSourceObject state.Source) {
+	stateSourceObject.Load(0, &r.refCount)
+	stateSourceObject.AfterLoad(r.afterLoad)
+}
+
+func init() {
+	state.Register((*Registry)(nil))
+	state.Register((*Shm)(nil))
+	state.Register((*ShmRefs)(nil))
+}