linux-kernel - Re: [PATCH net-next] devlink: Require devlink lock during device reload

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Message-ID: <20211108153126.1f3a8fe8@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 8 Nov 2021 15:31:26 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Ido Schimmel <idosch@...sch.org>, Jiri Pirko <jiri@...nulli.us>,
        "David S . Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...dia.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, edwin.peer@...adcom.com
Subject: Re: [PATCH net-next] devlink: Require devlink lock during device
 reload

On Mon, 8 Nov 2021 21:58:36 +0200 Leon Romanovsky wrote:
> > > > nfp will benefit from the simplified locking as well, and so will bnxt,
> > > > although I'm not sure the maintainers will opt for using devlink framework
> > > > due to the downstream requirements.    
> > > 
> > > Exactly why devlink should be fixed first.  
> > 
> > If by "fixed first" you mean it needs 5 locks to be added and to remove
> > any guarantees on sub-object lifetime then no thanks.  
> 
> How do you plan to fix pernet_ops_rwsem lock? By exposing devlink state
> to the drivers? By providing unlocked version of unregister_netdevice_notifier?
> 
> This simple scenario has deadlocks:
> sudo ip netns add n1
> sudo devlink dev reload pci/0000:00:09.0 netns n1
> sudo ip netns del n1

Okay - I'm not sure why you're asking me this. This is not related to
devlink locking as far as I can tell. Neither are you fixing this
problem in your own RFC.

You'd need to tell me more about what the notifier is used for (I see
RoCE in the call trace). I don't understand why you need to re-register 
a global (i.e. not per netns) notifier when devlink is switching name
spaces.