internal/pty/pty.go

@@ -6,13 +6,22 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"sync"
 	"syscall"
 
 	cpty "github.com/creack/pty"
 )
 
 // PTY holds a child process attached to a pseudo-terminal master fd.
+//
+// mu guards the master field only. Read/Write/Resize capture the *os.File
+// under the lock and then do the (potentially blocking) I/O without holding
+// it, so Close can swap master to nil and close the fd concurrently — closing
+// the captured *os.File unblocks an in-flight Read. This avoids a data race
+// between pumpChild's Read and Session.Shutdown's Close, which the daemon now
+// hits routinely (daemon stop, not just process exit).
 type PTY struct {
+	mu     sync.Mutex
 	master *os.File
 	cmd    *exec.Cmd
 }
@@ -45,24 +54,33 @@ func Start(argv []string, env []string, workDir string, cols, rows uint16) (*PTY
 }
 
 func (p *PTY) Read(b []byte) (int, error) {
-	if p.master == nil {
+	p.mu.Lock()
+	m := p.master
+	p.mu.Unlock()
+	if m == nil {
 		return 0, io.ErrClosedPipe
 	}
-	return p.master.Read(b)
+	return m.Read(b)
 }
 
 func (p *PTY) Write(b []byte) (int, error) {
-	if p.master == nil {
+	p.mu.Lock()
+	m := p.master
+	p.mu.Unlock()
+	if m == nil {
 		return 0, io.ErrClosedPipe
 	}
-	return p.master.Write(b)
+	return m.Write(b)
 }
 
 func (p *PTY) Resize(cols, rows uint16) error {
-	if p.master == nil {
+	p.mu.Lock()
+	m := p.master
+	p.mu.Unlock()
+	if m == nil {
 		return io.ErrClosedPipe
 	}
-	return cpty.Setsize(p.master, &cpty.Winsize{Cols: cols, Rows: rows})
+	return cpty.Setsize(m, &cpty.Winsize{Cols: cols, Rows: rows})
 }
 
 // Wait blocks until the child exits and returns its exit error if any.
@@ -83,12 +101,15 @@ func (p *PTY) Pid() int {
 
 // Close terminates the child (best effort) and releases the master fd.
 func (p *PTY) Close() error {
+	p.mu.Lock()
+	m := p.master
+	p.master = nil
+	p.mu.Unlock()
 	var firstErr error
-	if p.master != nil {
+	if m != nil {
-		if err := p.master.Close(); err != nil && firstErr == nil {
+		if err := m.Close(); err != nil {
 			firstErr = err
 		}
-		p.master = nil
 	}
 	if p.cmd != nil && p.cmd.Process != nil {
 		pid := p.cmd.Process.Pid