diff --git a/src/os/dir_darwin.go b/src/os/dir_darwin.go
index e6d5bda24b..91b67d8d61 100644
--- a/src/os/dir_darwin.go
+++ b/src/os/dir_darwin.go
@@ -25,16 +25,24 @@ func (d *dirInfo) close() {
 }
 
 func (f *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
-	if f.dirinfo == nil {
+	// If this file has no dirinfo, create one.
+	var d *dirInfo
+	for {
+		d = f.dirinfo.Load()
+		if d != nil {
+			break
+		}
 		dir, call, errno := f.pfd.OpenDir()
 		if errno != nil {
 			return nil, nil, nil, &PathError{Op: call, Path: f.name, Err: errno}
 		}
-		f.dirinfo = &dirInfo{
-			dir: dir,
+		d = &dirInfo{dir: dir}
+		if f.dirinfo.CompareAndSwap(nil, d) {
+			break
 		}
+		// We lost the race: try again.
+		d.close()
 	}
-	d := f.dirinfo
 
 	size := n
 	if size <= 0 {
diff --git a/src/os/dir_plan9.go b/src/os/dir_plan9.go
index 6ea5940e71..ab5c1efce5 100644
--- a/src/os/dir_plan9.go
+++ b/src/os/dir_plan9.go
@@ -12,10 +12,14 @@ import (
 
 func (file *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
 	// If this file has no dirinfo, create one.
-	if file.dirinfo == nil {
-		file.dirinfo = new(dirInfo)
+	d := file.dirinfo.Load()
+	if d == nil {
+		d = new(dirInfo)
+		file.dirinfo.Store(d)
 	}
-	d := file.dirinfo
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
 	size := n
 	if size <= 0 {
 		size = 100
diff --git a/src/os/dir_unix.go b/src/os/dir_unix.go
index e14edc13dc..7680be7799 100644
--- a/src/os/dir_unix.go
+++ b/src/os/dir_unix.go
@@ -17,6 +17,7 @@ import (
 
 // Auxiliary information if the File describes a directory
 type dirInfo struct {
+	mu   sync.Mutex
 	buf  *[]byte // buffer for directory I/O
 	nbuf int     // length of buf; return value from Getdirentries
 	bufp int     // location of next record in buf.
@@ -43,13 +44,16 @@ func (d *dirInfo) close() {
 }
 
 func (f *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
-	// If this file has no dirinfo, create one.
-	if f.dirinfo == nil {
-		f.dirinfo = new(dirInfo)
+	// If this file has no dirInfo, create one.
+	d := f.dirinfo.Load()
+	if d == nil {
+		d = new(dirInfo)
+		f.dirinfo.Store(d)
 	}
-	d := f.dirinfo
+	d.mu.Lock()
+	defer d.mu.Unlock()
 	if d.buf == nil {
-		f.dirinfo.buf = dirBufPool.Get().(*[]byte)
+		d.buf = dirBufPool.Get().(*[]byte)
 	}
 
 	// Change the meaning of n for the implementation below.
diff --git a/src/os/dir_windows.go b/src/os/dir_windows.go
index 0dbc3aec3e..52d5acda2a 100644
--- a/src/os/dir_windows.go
+++ b/src/os/dir_windows.go
@@ -16,6 +16,7 @@ import (
 
 // Auxiliary information if the File describes a directory
 type dirInfo struct {
+	mu sync.Mutex
 	// buf is a slice pointer so the slice header
 	// does not escape to the heap when returning
 	// buf to dirBufPool.
@@ -93,14 +94,27 @@ func (d *dirInfo) init(h syscall.Handle) {
 }
 
 func (file *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
-	if file.dirinfo == nil {
-		file.dirinfo = new(dirInfo)
-		file.dirinfo.init(file.pfd.Sysfd)
+	// If this file has no dirInfo, create one.
+	var d *dirInfo
+	for {
+		d = file.dirinfo.Load()
+		if d != nil {
+			break
+		}
+		d = new(dirInfo)
+		d.init(file.pfd.Sysfd)
+		if file.dirinfo.CompareAndSwap(nil, d) {
+			break
+		}
+		// We lost the race: try again.
+		d.close()
 	}
-	d := file.dirinfo
+	d.mu.Lock()
+	defer d.mu.Unlock()
 	if d.buf == nil {
 		d.buf = dirBufPool.Get().(*[]byte)
 	}
+
 	wantAll := n <= 0
 	if wantAll {
 		n = -1
diff --git a/src/os/file.go b/src/os/file.go
index a41aac9bb3..ec8ad70660 100644
--- a/src/os/file.go
+++ b/src/os/file.go
@@ -34,9 +34,13 @@
 //	}
 //	fmt.Printf("read %d bytes: %q\n", count, data[:count])
 //
-// Note: The maximum number of concurrent operations on a File may be limited by
-// the OS or the system. The number should be high, but exceeding it may degrade
-// performance or cause other issues.
+// # Concurrency
+//
+// The methods of [File] correspond to file system operations. All are
+// safe for concurrent use. The maximum number of concurrent
+// operations on a File may be limited by the OS or the system. The
+// number should be high, but exceeding it may degrade performance or
+// cause other issues.
 package os
 
 import (
@@ -53,6 +57,8 @@ import (
 )
 
 // Name returns the name of the file as presented to Open.
+//
+// It is safe to call Name after [Close].
 func (f *File) Name() string { return f.name }
 
 // Stdin, Stdout, and Stderr are open Files pointing to the standard input,
@@ -279,7 +285,7 @@ func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
 		return 0, err
 	}
 	r, e := f.seek(offset, whence)
-	if e == nil && f.dirinfo != nil && r != 0 {
+	if e == nil && f.dirinfo.Load() != nil && r != 0 {
 		e = syscall.EISDIR
 	}
 	if e != nil {
diff --git a/src/os/file_plan9.go b/src/os/file_plan9.go
index 477674b80a..fc9c89f09a 100644
--- a/src/os/file_plan9.go
+++ b/src/os/file_plan9.go
@@ -9,6 +9,8 @@ import (
 	"internal/poll"
 	"io"
 	"runtime"
+	"sync"
+	"sync/atomic"
 	"syscall"
 	"time"
 )
@@ -26,8 +28,8 @@ type file struct {
 	fdmu       poll.FDMutex
 	fd         int
 	name       string
-	dirinfo    *dirInfo // nil unless directory being read
-	appendMode bool     // whether file is opened for appending
+	dirinfo    atomic.Pointer[dirInfo] // nil unless directory being read
+	appendMode bool                    // whether file is opened for appending
 }
 
 // Fd returns the integer Plan 9 file descriptor referencing the open file.
@@ -60,6 +62,7 @@ func NewFile(fd uintptr, name string) *File {
 
 // Auxiliary information if the File describes a directory
 type dirInfo struct {
+	mu   sync.Mutex
 	buf  [syscall.STATMAX]byte // buffer for directory I/O
 	nbuf int                   // length of buf; return value from Read
 	bufp int                   // location of next record in buf.
@@ -349,11 +352,9 @@ func (f *File) seek(offset int64, whence int) (ret int64, err error) {
 		return 0, err
 	}
 	defer f.decref()
-	if f.dirinfo != nil {
-		// Free cached dirinfo, so we allocate a new one if we
-		// access this file as a directory again. See #35767 and #37161.
-		f.dirinfo = nil
-	}
+	// Free cached dirinfo, so we allocate a new one if we
+	// access this file as a directory again. See #35767 and #37161.
+	f.dirinfo.Store(nil)
 	return syscall.Seek(f.fd, offset, whence)
 }
 
diff --git a/src/os/file_unix.go b/src/os/file_unix.go
index f36028bfcb..8ecbffa81f 100644
--- a/src/os/file_unix.go
+++ b/src/os/file_unix.go
@@ -11,6 +11,7 @@ import (
 	"internal/syscall/unix"
 	"io/fs"
 	"runtime"
+	"sync/atomic"
 	"syscall"
 	_ "unsafe" // for go:linkname
 )
@@ -58,10 +59,10 @@ func rename(oldname, newname string) error {
 type file struct {
 	pfd         poll.FD
 	name        string
-	dirinfo     *dirInfo // nil unless directory being read
-	nonblock    bool     // whether we set nonblocking mode
-	stdoutOrErr bool     // whether this is stdout or stderr
-	appendMode  bool     // whether file is opened for appending
+	dirinfo     atomic.Pointer[dirInfo] // nil unless directory being read
+	nonblock    bool                    // whether we set nonblocking mode
+	stdoutOrErr bool                    // whether this is stdout or stderr
+	appendMode  bool                    // whether file is opened for appending
 }
 
 // Fd returns the integer Unix file descriptor referencing the open file.
@@ -325,9 +326,8 @@ func (file *file) close() error {
 	if file == nil {
 		return syscall.EINVAL
 	}
-	if file.dirinfo != nil {
-		file.dirinfo.close()
-		file.dirinfo = nil
+	if info := file.dirinfo.Swap(nil); info != nil {
+		info.close()
 	}
 	var err error
 	if e := file.pfd.Close(); e != nil {
@@ -347,11 +347,10 @@ func (file *file) close() error {
 // relative to the current offset, and 2 means relative to the end.
 // It returns the new offset and an error, if any.
 func (f *File) seek(offset int64, whence int) (ret int64, err error) {
-	if f.dirinfo != nil {
+	if info := f.dirinfo.Swap(nil); info != nil {
 		// Free cached dirinfo, so we allocate a new one if we
 		// access this file as a directory again. See #35767 and #37161.
-		f.dirinfo.close()
-		f.dirinfo = nil
+		info.close()
 	}
 	ret, err = f.pfd.Seek(offset, whence)
 	runtime.KeepAlive(f)
diff --git a/src/os/file_windows.go b/src/os/file_windows.go
index 6ee15eb993..d883eb5cb2 100644
--- a/src/os/file_windows.go
+++ b/src/os/file_windows.go
@@ -11,6 +11,7 @@ import (
 	"internal/syscall/windows"
 	"runtime"
 	"sync"
+	"sync/atomic"
 	"syscall"
 	"unsafe"
 )
@@ -25,8 +26,8 @@ const _UTIME_OMIT = -1
 type file struct {
 	pfd        poll.FD
 	name       string
-	dirinfo    *dirInfo // nil unless directory being read
-	appendMode bool     // whether file is opened for appending
+	dirinfo    atomic.Pointer[dirInfo] // nil unless directory being read
+	appendMode bool                    // whether file is opened for appending
 }
 
 // Fd returns the Windows handle referencing the open file.
@@ -127,9 +128,8 @@ func (file *file) close() error {
 	if file == nil {
 		return syscall.EINVAL
 	}
-	if file.dirinfo != nil {
-		file.dirinfo.close()
-		file.dirinfo = nil
+	if info := file.dirinfo.Swap(nil); info != nil {
+		info.close()
 	}
 	var err error
 	if e := file.pfd.Close(); e != nil {
@@ -149,11 +149,10 @@ func (file *file) close() error {
 // relative to the current offset, and 2 means relative to the end.
 // It returns the new offset and an error, if any.
 func (f *File) seek(offset int64, whence int) (ret int64, err error) {
-	if f.dirinfo != nil {
+	if info := f.dirinfo.Swap(nil); info != nil {
 		// Free cached dirinfo, so we allocate a new one if we
 		// access this file as a directory again. See #35767 and #37161.
-		f.dirinfo.close()
-		f.dirinfo = nil
+		info.close()
 	}
 	ret, err = f.pfd.Seek(offset, whence)
 	runtime.KeepAlive(f)
diff --git a/src/os/types.go b/src/os/types.go
index 66eb8bc8cb..d51a458f44 100644
--- a/src/os/types.go
+++ b/src/os/types.go
@@ -13,6 +13,8 @@ import (
 func Getpagesize() int { return syscall.Getpagesize() }
 
 // File represents an open file descriptor.
+//
+// The methods of File are safe for concurrent use.
 type File struct {
 	*file // os specific
 }