linux-kernel - Re: [PATCH net-next 2/7] net: mscc: ocelot: remove struct ocelot_mm_state

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Message-ID: <dceab485-1d51-0340-e5cc-8929901c64ad@gmail.com>
Date:   Mon, 17 Apr 2023 05:56:58 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/7] net: mscc: ocelot: remove struct
 ocelot_mm_state :: lock



On 4/15/2023 10:05 AM, Vladimir Oltean wrote:
> Unfortunately, the workarounds for the hardware bugs make it pointless
> to keep fine-grained locking for the MAC Merge state of each port.
> 
> Our vsc9959_cut_through_fwd() implementation requires
> ocelot->fwd_domain_lock to be held, in order to serialize with changes
> to the bridging domains and to port speed changes (which affect which
> ports can be cut-through). Simultaneously, the traffic classes which can
> be cut-through cannot be preemptible at the same time, and this will
> depend on the MAC Merge layer state (which changes from threaded
> interrupt context).
> 
> Since vsc9959_cut_through_fwd() would have to hold the mm->lock of all
> ports for a correct and race-free implementation with respect to
> ocelot_mm_irq(), in practice it means that any time a port's mm->lock is
> held, it would potentially block holders of ocelot->fwd_domain_lock.
> 
> In the interest of simple locking rules, make all MAC Merge layer state
> changes (and preemptible traffic class changes) be serialized by the
> ocelot->fwd_domain_lock.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

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