netdev - Re: [PATCH wpan-next v3 11/11] net: mac802154: Add a warning in the slow path

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Message-ID: <CAK-6q+hPWRUobMATaxD6rZ1zfQUnS_6pMacr+rKVHRAWe1xzSQ@mail.gmail.com>
Date:   Tue, 17 May 2022 20:52:35 -0400
From:   Alexander Aring <aahringo@...hat.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan - ML <linux-wpan@...r.kernel.org>,
        David Girault <david.girault@...vo.com>,
        Romuald Despres <romuald.despres@...vo.com>,
        Frederic Blain <frederic.blain@...vo.com>,
        Nicolas Schodet <nico@...fr.eu.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH wpan-next v3 11/11] net: mac802154: Add a warning in the
 slow path

Hi,

On Tue, May 17, 2022 at 12:35 PM Miquel Raynal
<miquel.raynal@...tlin.com> wrote:
>
> In order to be able to detect possible conflicts between the net
> interface core and the ieee802154 core, let's add a warning in the slow
> path: we want to be sure that whenever we start an asynchronous MLME
> transmission (which can be fully asynchronous) the net core somehow
> agrees that this transmission is possible, ie. the device was not
> stopped. Warning in this case would allow us to track down more easily
> possible issues with the MLME logic if we ever get reports.
>
> Unlike in the hot path, such a situation cannot be handled.
>
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
>  net/mac802154/tx.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/net/mac802154/tx.c b/net/mac802154/tx.c
> index e36aca788ea2..53a8be822e33 100644
> --- a/net/mac802154/tx.c
> +++ b/net/mac802154/tx.c
> @@ -132,6 +132,25 @@ int ieee802154_sync_and_hold_queue(struct ieee802154_local *local)
>         return ret;
>  }
>
> +static bool ieee802154_netif_is_down(struct ieee802154_local *local)
> +{
> +       struct ieee802154_sub_if_data *sdata;
> +       bool is_down = true;
> +
> +       rcu_read_lock();
> +       list_for_each_entry_rcu(sdata, &local->interfaces, list) {
> +               if (!sdata->dev)
> +                       continue;
> +
> +               is_down = !(sdata->dev->flags & IFF_UP);
> +               if (is_down)
> +                       break;

I thought that the helper would be "netif_running()". It seems there
are multiple ways to check if an interface is up.

> +       }
> +       rcu_read_unlock();
> +
> +       return is_down;
> +}
> +
>  static int ieee802154_mlme_op_pre(struct ieee802154_local *local)
>  {
>         return ieee802154_sync_and_hold_queue(local);
> @@ -150,6 +169,12 @@ static int ieee802154_mlme_tx(struct ieee802154_local *local, struct sk_buff *sk
>         if (!local->open_count)
>                 return -EBUSY;
>
> +       /* Warn if the ieee802154 core thinks MLME frames can be sent while the
> +        * net interface expects this cannot happen.
> +        */
> +       if (WARN_ON_ONCE(ieee802154_netif_is_down(local)))
> +               return -EHOSTDOWN;

maybe also ENETDOWN? Also there is a missing rtnl_unlock().

- Alex