Go: Data Race Quiz! Shadowing or Stomping?

data_race_quiz.go

package main

import (
	"context"
	"io"
	"time"
)

type uploader struct{}

// Shadowing or Stomping?
// TODO: In this function, which lines cause a data race, specifically a simultaneous read and write to the same data?
func (u *uploader) BackupAndUpload(ctx context.Context) (string, error) {
	pr, pw := io.Pipe()
	go func() {
		_, err := u.Backup(ctx, pw)
		pw.CloseWithError(err)
	}()
	ctx, cancel := context.WithTimeout(ctx, 10*time.Minute)
	defer cancel()
	return u.Upload(ctx, pr)
}

Hint: Line 15, _, err := u.Backup(ctx, pw), potentially reads from X, while line 18, ctx, cancel := context.WithTimeout(ctx, 10*time.Minute), writes to X at the same time.