netdev - Re: [PATCH net-next] netdevsim: Register and unregister devlink traps on probe/remove device

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Message-ID: <20211027122824.5bebb9a4@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 27 Oct 2021 12:28:24 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Ido Schimmel <idosch@...sch.org>,
        "David S . Miller" <davem@...emloft.net>,
        Ido Schimmel <idosch@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org,
        syzbot+93d5accfaefceedf43c1@...kaller.appspotmail.com,
        Edwin Peer <edwin.peer@...adcom.com>
Subject: Re: [PATCH net-next] netdevsim: Register and unregister devlink
 traps on probe/remove device

On Wed, 27 Oct 2021 22:15:41 +0300 Leon Romanovsky wrote:
> One of the outcomes is that such chain usually prevents from us to ensure
> proper locking annotation.
> 
> Let's take as an example devlink_trap_policers_register().
> In some drivers, it is called before device_register() and we don't need
> any locks at all, because we are in initialization flow.
> 
> In mlxsw, it is called during devlink reload, and we don't really need to
> lock it too, because we were supposed to lock everything for the reload.
> 
> However, for the mlxsw, we created devlink_trap_policers_register() to be
> dynamic, so we must lock devlink->lock, as we don't know how other users
> of this API will use it.
> 
> In the reality, no one uses it dynamically except mlxsw and we stuck
> with function that calls to useless lock without us able to properly
> annotate it with an invitation to misuse.
> 
> It is an example of layering problem, there are many more subtle issues
> like this that require some cabal knowledge of proper locks to make it
> is safe.

Now that you made me express my opinion I started feeling attached to
my way of thinking :) Let me try to convert devlink core, netdevsim and
nfp to devlink instance locking and see how far I can get...