Fix data race in tty.queue.readableSize.

We were setting queue.readable without holding the lock.

PiperOrigin-RevId: 290306922

pkg/sentry/fs/tty/line_discipline.go

@@ -140,8 +140,10 @@ func (l *lineDiscipline) setTermios(ctx context.Context, io usermem.IO, args arc
 	// buffer to its read buffer. Anything already in the read buffer is
 	// now readable.
 	if oldCanonEnabled && !l.termios.LEnabled(linux.ICANON) {
-		l.inQueue.pushWaitBuf(l)
+		l.inQueue.mu.Lock()
+		l.inQueue.pushWaitBufLocked(l)
 		l.inQueue.readable = true
+		l.inQueue.mu.Unlock()
 		l.slaveWaiter.Notify(waiter.EventIn)
 	}
 

pkg/sentry/fs/tty/queue.go

@@ -197,16 +197,9 @@ func (q *queue) writeBytes(b []byte, l *lineDiscipline) {
 	q.pushWaitBufLocked(l)
 }
 
-// pushWaitBuf fills the queue's read buffer with data from the wait buffer.
+// pushWaitBufLocked fills the queue's read buffer with data from the wait
+// buffer.
 //
-// Preconditions:
-// * l.termiosMu must be held for reading.
-func (q *queue) pushWaitBuf(l *lineDiscipline) int {
-	q.mu.Lock()
-	defer q.mu.Unlock()
-	return q.pushWaitBufLocked(l)
-}
-
 // Preconditions:
 // * l.termiosMu must be held for reading.
 // * q.mu must be locked.