Merge release-20210503.0-47-g07e32fa69 (automated)

6 files changed, 48 insertions, 0 deletions

diff --git a/pkg/sentry/kernel/fd_table_refs.go b/pkg/sentry/kernel/fd_table_refs.go
index ddbe50261..9b0b1628e 100644
--- a/pkg/sentry/kernel/fd_table_refs.go
+++ b/pkg/sentry/kernel/fd_table_refs.go
@@ -20,6 +20,14 @@ var FDTableobj *FDTable
 // 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 FDTableRefs struct {
 	// refCount is composed of two fields:
diff --git a/pkg/sentry/kernel/fs_context_refs.go b/pkg/sentry/kernel/fs_context_refs.go
index d97c82fc9..484c20683 100644
--- a/pkg/sentry/kernel/fs_context_refs.go
+++ b/pkg/sentry/kernel/fs_context_refs.go
@@ -20,6 +20,14 @@ var FSContextobj *FSContext
 // 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 FSContextRefs struct {
 	// refCount is composed of two fields:
diff --git a/pkg/sentry/kernel/ipc_namespace_refs.go b/pkg/sentry/kernel/ipc_namespace_refs.go
index a2a2d3458..dd399aebd 100644
--- a/pkg/sentry/kernel/ipc_namespace_refs.go
+++ b/pkg/sentry/kernel/ipc_namespace_refs.go
@@ -20,6 +20,14 @@ var IPCNamespaceobj *IPCNamespace
 // 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 IPCNamespaceRefs struct {
 	// refCount is composed of two fields:
diff --git a/pkg/sentry/kernel/process_group_refs.go b/pkg/sentry/kernel/process_group_refs.go
index 51b0fcd34..e29b2ea3a 100644
--- a/pkg/sentry/kernel/process_group_refs.go
+++ b/pkg/sentry/kernel/process_group_refs.go
@@ -20,6 +20,14 @@ var ProcessGroupobj *ProcessGroup
 // 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 ProcessGroupRefs struct {
 	// refCount is composed of two fields:
diff --git a/pkg/sentry/kernel/session_refs.go b/pkg/sentry/kernel/session_refs.go
index 84919943d..0186a0e6d 100644
--- a/pkg/sentry/kernel/session_refs.go
+++ b/pkg/sentry/kernel/session_refs.go
@@ -20,6 +20,14 @@ var Sessionobj *Session
 // 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 SessionRefs struct {
 	// refCount is composed of two fields:
diff --git a/pkg/sentry/kernel/shm/shm_refs.go b/pkg/sentry/kernel/shm/shm_refs.go
index e1c9167ad..f832c1a99 100644
--- a/pkg/sentry/kernel/shm/shm_refs.go
+++ b/pkg/sentry/kernel/shm/shm_refs.go
@@ -20,6 +20,14 @@ 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: