From: Tobias Waldekranz <tobias@waldekranz.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: davem@davemloft.net, kuba@kernel.org, vivien.didelot@gmail.com,
f.fainelli@gmail.com, olteanv@gmail.com, j.vosburgh@gmail.com,
vfalico@gmail.com, andy@greyhouse.net, netdev@vger.kernel.org
Subject: Re: [PATCH v3 net-next 2/4] net: dsa: Link aggregation support
Date: Mon, 07 Dec 2020 22:19:47 +0100 [thread overview]
Message-ID: <87v9dd5n64.fsf@waldekranz.com> (raw)
In-Reply-To: <20201204022025.GC2414548@lunn.ch>
On Fri, Dec 04, 2020 at 03:20, Andrew Lunn <andrew@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
next prev parent reply other threads:[~2020-12-07 21:20 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-02 9:13 [PATCH v3 net-next 0/4] net: dsa: Link aggregation support Tobias Waldekranz
2020-12-02 9:13 ` [PATCH v3 net-next 1/4] net: bonding: Notify ports about their initial state Tobias Waldekranz
2020-12-02 19:09 ` Jay Vosburgh
2020-12-02 21:52 ` Tobias Waldekranz
2020-12-03 0:39 ` Jay Vosburgh
2020-12-03 8:16 ` Tobias Waldekranz
2020-12-02 9:13 ` [PATCH v3 net-next 2/4] net: dsa: Link aggregation support Tobias Waldekranz
2020-12-02 10:07 ` Vladimir Oltean
2020-12-02 10:51 ` Tobias Waldekranz
2020-12-02 18:58 ` Jakub Kicinski
2020-12-02 21:29 ` Tobias Waldekranz
2020-12-02 21:32 ` Vladimir Oltean
2020-12-03 16:24 ` Vladimir Oltean
2020-12-03 20:53 ` Tobias Waldekranz
2020-12-03 21:09 ` Andrew Lunn
2020-12-03 21:35 ` Tobias Waldekranz
2020-12-04 0:35 ` Vladimir Oltean
2020-12-03 21:57 ` Vladimir Oltean
2020-12-03 23:12 ` Tobias Waldekranz
2020-12-04 0:56 ` Vladimir Oltean
2020-12-07 21:49 ` Tobias Waldekranz
2020-12-04 1:33 ` Andrew Lunn
2020-12-04 4:18 ` Florian Fainelli
2020-12-07 21:56 ` Tobias Waldekranz
2020-12-03 20:48 ` Vladimir Oltean
2020-12-04 2:20 ` Andrew Lunn
2020-12-07 21:19 ` Tobias Waldekranz [this message]
2020-12-07 23:26 ` Andrew Lunn
2020-12-09 8:57 ` Tobias Waldekranz
2020-12-09 14:27 ` Andrew Lunn
2020-12-09 15:21 ` Tobias Waldekranz
2020-12-09 23:03 ` Andrew Lunn
2020-12-04 4:04 ` Florian Fainelli
2020-12-08 11:23 ` Vladimir Oltean
2020-12-08 15:33 ` Tobias Waldekranz
2020-12-08 16:37 ` Vladimir Oltean
2020-12-09 8:37 ` Tobias Waldekranz
2020-12-09 10:53 ` Vladimir Oltean
2020-12-09 14:11 ` Tobias Waldekranz
2020-12-09 16:04 ` Vladimir Oltean
2020-12-09 22:01 ` Tobias Waldekranz
2020-12-09 22:21 ` Vladimir Oltean
2020-12-10 10:18 ` Tobias Waldekranz
2020-12-09 22:59 ` Andrew Lunn
2020-12-10 1:05 ` Vladimir Oltean
2020-12-09 14:23 ` Andrew Lunn
2020-12-09 23:17 ` Vladimir Oltean
2020-12-08 17:26 ` Andrew Lunn
2020-12-11 20:50 ` Tobias Waldekranz
2020-12-12 14:26 ` Vladimir Oltean
2020-12-13 21:18 ` Tobias Waldekranz
2020-12-14 0:12 ` Vladimir Oltean
2020-12-14 11:42 ` Ido Schimmel
2020-12-16 15:15 ` Tobias Waldekranz
2020-12-16 18:48 ` Ido Schimmel
2020-12-14 9:41 ` Tobias Waldekranz
2020-12-02 9:13 ` [PATCH v3 net-next 3/4] net: dsa: mv88e6xxx: " Tobias Waldekranz
2020-12-02 9:13 ` [PATCH v3 net-next 4/4] net: dsa: tag_dsa: Support reception of packets from LAG devices Tobias Waldekranz
2020-12-04 3:58 ` Florian Fainelli
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