Re: [PATCH] net: make netdev_wait_allrefs wake-able

[Eric Dumazet]

On Thu, Sep 17, 2020 at 8:33 AM Francesco Ruggeri <fruggeri@xxxxxxxxxx> wrote:
>
> >  static inline void dev_put(struct net_device *dev)
> >  {
> > +       struct task_struct *destroy_task = dev->destroy_task;
> > +
> >         this_cpu_dec(*dev->pcpu_refcnt);
> > +       if (destroy_task)
> > +               wake_up_process(destroy_task);
> >  }
>
> I just realized that this introduces a race, if dev_put drops the last
> reference, an already running netdev_wait_allrefs runs to completion
> and then dev_put tries to wake it up.
> Any suggestions on how to avoid this without resorting to
> locking?
>

Honestly I would not touch dev_put() at all.

Simply change the msleep(250) to something better, with maybe
exponential backoff.