linux-kernel - Re: [PATCH] net: make netdev_wait

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Message-ID: <CA+HUmGjX4_4_UXWNn=EehQ_3QtFPZq8RJU146r-nc0nA8apx7w@mail.gmail.com>
Date:   Wed, 16 Sep 2020 23:33:21 -0700
From:   Francesco Ruggeri <fruggeri@...sta.com>
To:     open list <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, xiyou.wangcong@...il.com,
        ap420073@...il.com, andriin@...com,
        Eric Dumazet <edumazet@...gle.com>, jiri@...lanox.com,
        ast@...nel.org, Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Francesco Ruggeri <fruggeri@...sta.com>
Subject: Re: [PATCH] net: make netdev_wait_allrefs wake-able

>  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?

Thanks,
Francesco