netdev - Re: [RFC PATCH v7 02/16] net: dsa: replay master state events in dsa_tree_{setup,teardown}

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Message-ID: <cba946ff-5ba4-b2af-118c-b1d0a7669450@gmail.com>
Date:   Tue, 25 Jan 2022 19:27:35 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Ansuel Smith <ansuelsmth@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [RFC PATCH v7 02/16] net: dsa: replay master state events in
 dsa_tree_{setup,teardown}_master



On 1/22/2022 5:33 PM, Ansuel Smith wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> In order for switch driver to be able to make simple and reliable use of
> the master tracking operations, they must also be notified of the
> initial state of the DSA master, not just of the changes. This is
> because they might enable certain features only during the time when
> they know that the DSA master is up and running.
> 
> Therefore, this change explicitly checks the state of the DSA master
> under the same rtnl_mutex as we were holding during the
> dsa_master_setup() and dsa_master_teardown() call. The idea being that
> if the DSA master became operational in between the moment in which it
> became a DSA master (dsa_master_setup set dev->dsa_ptr) and the moment
> when we checked for the master being up, there is a chance that we
> would emit a ->master_state_change() call with no actual state change.
> We need to avoid that by serializing the concurrent netdevice event with
> us. If the netdevice event started before, we force it to finish before
> we begin, because we take rtnl_lock before making netdev_uses_dsa()
> return true. So we also handle that early event and do nothing on it.
> Similarly, if the dev_open() attempt is concurrent with us, it will
> attempt to take the rtnl_mutex, but we're holding it. We'll see that
> the master flag IFF_UP isn't set, then when we release the rtnl_mutex
> we'll process the NETDEV_UP notifier.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian