netdev - Re: [PATCH] net: dsa: Fix off-by-one number of calls to devlink_port

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Date:   Mon, 02 Sep 2019 12:00:05 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     olteanv@...il.com
Cc:     f.fainelli@...il.com, vivien.didelot@...il.com, andrew@...n.ch,
        netdev@...r.kernel.org
Subject: Re: [PATCH] net: dsa: Fix off-by-one number of calls to
 devlink_port_unregister

From: Vladimir Oltean <olteanv@...il.com>
Date: Sat, 31 Aug 2019 15:46:19 +0300

> When a function such as dsa_slave_create fails, currently the following
> stack trace can be seen:
 ...
> devlink_free is complaining right here:
> 
> 	WARN_ON(!list_empty(&devlink->port_list));
> 
> This happens because devlink_port_unregister is no longer done right
> away in dsa_port_setup when a DSA_PORT_TYPE_USER has failed.
> Vivien said about this change that:
> 
>     Also no need to call devlink_port_unregister from within dsa_port_setup
>     as this step is inconditionally handled by dsa_port_teardown on error.
> 
> which is not really true. The devlink_port_unregister function _is_
> being called unconditionally from within dsa_port_setup, but not for
> this port that just failed, just for the previous ones which were set
> up.
> 
> ports_teardown:
> 	for (i = 0; i < port; i++)
> 		dsa_port_teardown(&ds->ports[i]);
> 
> Initially I was tempted to fix this by extending the "for" loop to also
> cover the port that failed during setup. But this could have potentially
> unforeseen consequences unrelated to devlink_port or even other types of
> ports than user ports, which I can't really test for. For example, if
> for some reason devlink_port_register itself would fail, then
> unconditionally unregistering it in dsa_port_teardown would not be a
> smart idea. The list might go on.
> 
> So just make dsa_port_setup undo the setup it had done upon failure, and
> let the for loop undo the work of setting up the previous ports, which
> are guaranteed to be brought up to a consistent state.
> 
> Fixes: 955222ca5281 ("net: dsa: use a single switch statement for port setup")
> Signed-off-by: Vladimir Oltean <olteanv@...il.com>

Applied to net-next, thanks.