Demonstrating Single-Variable-Locks are not enough...

locks.go

package main

import (
        "log"
        "sync"
)

var (
        wg sync.WaitGroup

        am sync.Mutex
        a  int

        bm sync.Mutex
        b  int
)

func withdraw(v int) {
        am.Lock()
        al := a
        am.Unlock()
        
        am.Lock()
        a = al - v
        am.Unlock()

        bm.Lock()
        bl := b
        bm.Unlock()

        bm.Lock()
        b = bl + v
        bm.Unlock()

        wg.Done()
}

func deposit(v int) {
        bm.Lock()
        bl := b
        bm.Unlock()

        bm.Lock()
        b = bl - v
        bm.Unlock()

        am.Lock()
        al := a
        am.Unlock()

        am.Lock()
        a = al + v
        am.Unlock()

        wg.Done()
}

func main() {
        counter := 0
        for {
                wg.Add(2)

                go withdraw(10)
                go deposit(5)

                wg.Wait()

                counter++
                if a+b != 0 {
                        log.Fatalf("Invariant failed in case %v with a+b == %v+%v", counter, a, b)
                }
        }
}