netdev - Re: [patch net-next 0/8] devlink: make sure devlink port registers/unregisters only for registered instance

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Date:   Mon, 5 Dec 2022 17:08:26 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, pabeni@...hat.com,
        edumazet@...gle.com, michael.chan@...adcom.com,
        ioana.ciornei@....com, dmichail@...gible.com,
        jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        tchornyi@...vell.com, tariqt@...dia.com, saeedm@...dia.com,
        leon@...nel.org, idosch@...dia.com, petrm@...dia.com,
        vladimir.oltean@....com, claudiu.manoil@....com,
        alexandre.belloni@...tlin.com, simon.horman@...igine.com,
        shannon.nelson@....com, brett.creeley@....com
Subject: Re: [patch net-next 0/8] devlink: make sure devlink port
 registers/unregisters only for registered instance

On Mon,  5 Dec 2022 16:22:49 +0100 Jiri Pirko wrote:
> Currently, the devlink_register() is called as the last thing during
> driver init phase. For devlink objects, this is fine as the
> notifications of objects creations are withheld to be send only after
> devlink instance is registered. Until devlink is registered it is not
> visible to userspace.
> 
> But if a  netdev is registered before, user gets a notification with
> a link to devlink, which is not visible to the user yet.
> This is the event order user sees:
>  * new netdev event over RT netlink
>  * new devlink event over devlink netlink
>  * new devlink_port event over devlink netlink
> 
> Also, this is not consistent with devlink port split or devlink reload
> flows, where user gets notifications in following order:
>  * new devlink event over devlink netlink
> and then during port split or reload operation:
>  * new devlink_port event over devlink netlink
>  * new netdev event over RT netlink
> 
> In this case, devlink port and related netdev are registered on already
> registered devlink instance.
> 
> Purpose of this patchset is to fix the drivers init flow so devlink port
> gets registered only after devlink instance is registered.

I didn't reply because I don't have much to add beyond what 
I've already said too many times. I prefer to move to my
initial full refcounting / full locking design. I haven't posted 
any patches because I figured it's too low priority and too risky
to be doing right before the merge window.

I agree that reordering is a good idea but not as a fix, and hopefully
without conditional locking in the drivers:

+		if (!reload)
+			devl_lock(devlink);
+		err = mlxsw_driver->ports_init(mlxsw_core);
+		if (!reload)
+			devl_unlock(devlink);