netdev - Re: [PATCH net-next v1] netdevsim: Forbid devlink reload when adding or deleting ports

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Date:   Thu, 5 Aug 2021 06:15:47 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Leon Romanovsky <leonro@...dia.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v1] netdevsim: Forbid devlink reload when
 adding or deleting ports

On Thu,  5 Aug 2021 14:05:41 +0300 Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
> 
> In order to remove complexity in devlink core related to
> devlink_reload_enable/disable, let's rewrite new_port/del_port
> logic to rely on internal to netdevsim lock.
> 
> We should protect only reload_down flow because it destroys nsim_dev,
> which is needed for nsim_dev_port_add/nsim_dev_port_del to hold
> port_list_lock.

I don't understand why we only have to protect reload_down.

What protects us from adding a port right after down? That'd hit a
destroyed mutex, up wipes the port list etc...

> +	nsim_bus_dev = nsim_dev->nsim_bus_dev;
> +	if (!mutex_trylock(&nsim_bus_dev->nsim_bus_reload_lock))
> +		return -EOPNOTSUPP;

Why not -EBUSY?