Priority-inheritance futex implementation

It is Implemented without the priority inheritance part given
that gVisor defers scheduling decisions to Go runtime and doesn't
have control over it.

PiperOrigin-RevId: 236989545
Change-Id: I714c8ca0798743ecf3167b14ffeb5cd834302560

2 files changed, 15 insertions, 0 deletions

diff --git a/pkg/sentry/usermem/bytes_io_unsafe.go b/pkg/sentry/usermem/bytes_io_unsafe.go
index 8bdf3a508..7add8bc82 100644
--- a/pkg/sentry/usermem/bytes_io_unsafe.go
+++ b/pkg/sentry/usermem/bytes_io_unsafe.go
@@ -37,3 +37,11 @@ func (b *BytesIO) CompareAndSwapUint32(ctx context.Context, addr Addr, old, new
 	}
 	return atomicbitops.CompareAndSwapUint32((*uint32)(unsafe.Pointer(&b.Bytes[int(addr)])), old, new), nil
 }
+
+// LoadUint32 implements IO.LoadUint32.
+func (b *BytesIO) LoadUint32(ctx context.Context, addr Addr, opts IOOpts) (uint32, error) {
+	if _, err := b.rangeCheck(addr, 4); err != nil {
+		return 0, err
+	}
+	return atomic.LoadUint32((*uint32)(unsafe.Pointer(&b.Bytes[int(addr)]))), nil
+}
diff --git a/pkg/sentry/usermem/usermem.go b/pkg/sentry/usermem/usermem.go
index 75ac4d22d..c3c9c153b 100644
--- a/pkg/sentry/usermem/usermem.go
+++ b/pkg/sentry/usermem/usermem.go
@@ -103,6 +103,13 @@ type IO interface {
 	// any following locks in the lock order. addr must be aligned to a 4-byte
 	// boundary.
 	CompareAndSwapUint32(ctx context.Context, addr Addr, old, new uint32, opts IOOpts) (uint32, error)
+
+	// LoadUint32 atomically loads the uint32 value at addr and returns it.
+	//
+	// Preconditions: The caller must not hold mm.MemoryManager.mappingMu or
+	// any following locks in the lock order. addr must be aligned to a 4-byte
+	// boundary.
+	LoadUint32(ctx context.Context, addr Addr, opts IOOpts) (uint32, error)
 }
 
 // IOOpts contains options applicable to all IO methods.