On Fri, Dec 04, 2020 at 03:20, Andrew Lunn <and...@lunn.ch> wrote:
>> +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.
I was mostly paranoid about the case where, for some reason, the list of
ports was empty due to an invalid DT or something. But I now see that
since num is not initialized, that would not have helped.
So, is my paranoia valid, i.e. fix is `unsigned int num = 0`? Or can
that never happen, i.e. fix is to initialize to UINT_MAX and remove
first 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!
The name is intentionally generic as it answers the question "can this
dp offload requests for this netdev?"
>> +{
>> + /* Switchdev offloading can be configured on: */
>> +
>> + if (dev == dp->slave)
>> + /* DSA ports directly connected to a bridge. */
>> + return true;
This condition is the normal case of a bridged port, i.e. no LAG
involved.
>> + if (dp->lag && dev == rtnl_dereference(dp->lag->dev))
>> + /* DSA ports connected to a bridge via a LAG */
>> + return true;
And then the indirect case of a bridged port under a LAG.
I am happy to take requests for a better name though.
>> + 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.
All writers of dst->lags.busy are serialized with respect to dsa_lag_put
(on rtnl_lock), and concurrent readers (dsa_lag_dev_by_id) start by
checking busy before reading lag->dev. To my understanding, WRITE_ONCE
would insert the proper fence to make sure busy was cleared before
clearing dev?
> Andrew
