[PATCH net v4] net: dsa: mt7530: fix .get_stats64 sleeping in atomic context

[Jakub Kicinski]

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---
net: dsa: mt7530: fix .get_stats64 sleeping in atomic context

This commit introduces a delayed workqueue to asynchronously poll MIB counters
for MDIO-connected switches. This caches the results so they can be returned
safely without sleeping in the atomic .get_stats64 callback.

> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> index b9423389c2ef..66bff861a921 100644
> --- a/drivers/net/dsa/mt7530.c
> +++ b/drivers/net/dsa/mt7530.c

[ ... ]

> @@ -3137,9 +3187,25 @@ mt753x_setup(struct dsa_switch *ds)
>  	if (ret && priv->irq_domain)
>  		mt7530_free_mdio_irq(priv);
>  
> +	if (!ret && priv->bus) {
> +		spin_lock_init(&priv->stats_lock);
> +		INIT_DELAYED_WORK(&priv->stats_work, mt7530_stats_poll);
> +		mt7530_stats_refresh(priv);
> +		schedule_delayed_work(&priv->stats_work,
> +				      MT7530_STATS_POLL_INTERVAL);
> +	}
> +
>  	return ret;
>  }

[ ... ]

> @@ -3409,6 +3476,9 @@ mt7530_remove_common(struct mt7530_priv *priv)
>  
>  	dsa_unregister_switch(priv->ds);
>  
> +	if (priv->bus)
> +		cancel_delayed_work_sync(&priv->stats_work);

Could this call cancel_delayed_work_sync() on an uninitialized work struct
if the driver is unbound before the DSA switch tree completes?

The priv->bus pointer is initialized during probe. However,
INIT_DELAYED_WORK() is only called in mt753x_setup(), which might never
execute if the DSA tree remains incomplete.

If the driver is unbound in this state, mt7530_remove_common() will evaluate
priv->bus as true and pass a zero-initialized work struct to
cancel_delayed_work_sync(). This usually triggers lockdep ("trying to
register non-static key") and debugobjects ("assert_init not available")
warnings.

Would it be better to move the INIT_DELAYED_WORK() call into the probe
path or track whether the setup function was actually completed?
-- 
pw-bot: cr