netdev - Re: [PATCH v3 net-next 2/4] net: dsa: Link aggregation support

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Date:   Fri, 4 Dec 2020 03:20:25 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     davem@...emloft.net, kuba@...nel.org, vivien.didelot@...il.com,
        f.fainelli@...il.com, olteanv@...il.com, j.vosburgh@...il.com,
        vfalico@...il.com, andy@...yhouse.net, netdev@...r.kernel.org
Subject: Re: [PATCH v3 net-next 2/4] net: dsa: Link aggregation support

> +static int dsa_tree_setup_lags(struct dsa_switch_tree *dst)
> +{
> +	struct dsa_port *dp;
> +	unsigned int num;
> +
> +	list_for_each_entry(dp, &dst->ports, list)
> +		num = dp->ds->num_lags;
> +
> +	list_for_each_entry(dp, &dst->ports, list)
> +		num = min(num, dp->ds->num_lags);

Do you really need to loop over the list twice? Cannot num be
initialised to UINT_MAX and then just do the second loop.

> +static inline bool dsa_port_can_offload(struct dsa_port *dp,
> +					struct net_device *dev)

That name is a bit generic. We have a number of different offloads.
The mv88E6060 cannot offload anything!

> +{
> +	/* Switchdev offloading can be configured on: */
> +
> +	if (dev == dp->slave)
> +		/* DSA ports directly connected to a bridge. */
> +		return true;
> +
> +	if (dp->lag && dev == rtnl_dereference(dp->lag->dev))
> +		/* DSA ports connected to a bridge via a LAG */
> +		return true;
> +
> +	return false;
> +}

> +static void dsa_lag_put(struct dsa_switch_tree *dst, struct dsa_lag *lag)
> +{
> +	if (!refcount_dec_and_test(&lag->refcount))
> +		return;
> +
> +	clear_bit(lag->id, dst->lags.busy);
> +	WRITE_ONCE(lag->dev, NULL);
> +	memset(lag, 0, sizeof(*lag));
> +}

I don't know what the locking is here, but wouldn't it be safer to
clear the bit last, after the memset and WRITE_ONCE.

    Andrew