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Date:   Mon, 7 Dec 2020 17:09:37 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        UNGLinuxDriver@...rochip.com,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        "Allan W . Nielsen" <allan.nielsen@...rochip.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Steen Hegelund <steen.hegelund@...rochip.com>
Subject: Re: [PATCH v3 net-next] net: mscc: ocelot: install MAC addresses in
 .ndo_set_rx_mode from process context

On Sat,  5 Dec 2020 02:43:15 +0200 Vladimir Oltean wrote:
> Currently ocelot_set_rx_mode calls ocelot_mact_learn directly, which has
> a very nice ocelot_mact_wait_for_completion at the end. Introduced in
> commit 639c1b2625af ("net: mscc: ocelot: Register poll timeout should be
> wall time not attempts"), this function uses readx_poll_timeout which
> triggers a lot of lockdep warnings and is also dangerous to use from
> atomic context, potentially leading to lockups and panics.
> 
> Steen Hegelund added a poll timeout of 100 ms for checking the MAC
> table, a duration which is clearly absurd to poll in atomic context.
> So we need to defer the MAC table access to process context, which we do
> via a dynamically allocated workqueue which contains all there is to
> know about the MAC table operation it has to do.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
> ---
> Changes in v3:
> - Dropped Fixes tag and retargeted to net-next
> - Dropped get_device/put_device since they don't offer real protection
> - Now allocating a private ordered workqueue which is drained on unbind
>   to avoid accessing freed memory
> 
> Changes in v2:
> - Added Fixes tag (it won't backport that far, but anyway)
> - Using get_device and put_device to avoid racing with unbind
> 
>  drivers/net/ethernet/mscc/ocelot.c     |  5 ++
>  drivers/net/ethernet/mscc/ocelot_net.c | 81 +++++++++++++++++++++++++-
>  include/soc/mscc/ocelot.h              |  2 +
>  3 files changed, 85 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> index abea8dd2b0cb..b9626eec8db6 100644
> --- a/drivers/net/ethernet/mscc/ocelot.c
> +++ b/drivers/net/ethernet/mscc/ocelot.c
> @@ -1513,6 +1513,10 @@ int ocelot_init(struct ocelot *ocelot)
>  	if (!ocelot->stats_queue)
>  		return -ENOMEM;
>  
> +	ocelot->owq = alloc_ordered_workqueue("ocelot-owq", WQ_MEM_RECLAIM);

Why MEM_RECLAIM ?

> +	if (!ocelot->owq)
> +		return -ENOMEM;

I don't think you can pass NULL to destroy_workqueue() so IDK how this
code does error handling (freeing of ocelot->stats_queue if owq fails).

>  	INIT_LIST_HEAD(&ocelot->multicast);
>  	INIT_LIST_HEAD(&ocelot->pgids);
>  	ocelot_mact_init(ocelot);
> @@ -1619,6 +1623,7 @@ void ocelot_deinit(struct ocelot *ocelot)
>  {
>  	cancel_delayed_work(&ocelot->stats_work);
>  	destroy_workqueue(ocelot->stats_queue);
> +	destroy_workqueue(ocelot->owq);
>  	mutex_destroy(&ocelot->stats_lock);
>  }

> +static int ocelot_enqueue_mact_action(struct ocelot *ocelot,
> +				      const struct ocelot_mact_work_ctx *ctx)
> +{
> +	struct ocelot_mact_work_ctx *w = kmalloc(sizeof(*w), GFP_ATOMIC);
> +
> +	if (!w)
> +		return -ENOMEM;
> +
> +	memcpy(w, ctx, sizeof(*w));

kmemdup()?

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