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

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Date:   Tue, 16 Nov 2021 07:57:09 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, Jiri Pirko <jiri@...dia.com>,
        Ido Schimmel <idosch@...sch.org>,
        "David S . Miller" <davem@...emloft.net>,
        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

Mon, Nov 15, 2021 at 04:09:31PM CET, jgg@...dia.com wrote:
>On Mon, Nov 15, 2021 at 03:42:58PM +0100, Jiri Pirko wrote:
>
>> >Sorry, I don't agree that registering a net notifier in an aux device
>> >probe function is non-standard or wrong.
>> 
>> Listening to events which happen in different namespaces and react to
>> them is the non-standard behaviour which I refered to. If you would not
>> need to do it, you could just use netns notofier which would solve your
>> issue. You know it.
>
>Huh?
>
>It calls the bog standard
>
> register_netdevice_notifier() 
>
>Like hundreds of other drivers do from their probe functions
>
>Which does:
>
>int register_netdevice_notifier(struct notifier_block *nb)
>{
>	struct net *net;
>	int err;
>
>	/* Close race with setup_net() and cleanup_net() */
>	down_write(&pernet_ops_rwsem);
>
>And deadlocks because devlink hols the pernet_ops_rwsem when it
>triggers reload in some paths.
>
>There is nothing wrong with a driver doing this standard pattern.
>
>There is only one place in the entire kernel calling the per-ns
>register_netdevice_notifier_dev_net() and it is burred inside another
>part of mlx5 for some reason..

Yep. I added it there to solve this deadlock.

>
>I believe Parav already looked at using that in rdma and it didn't
>work for some reason I've forgotten. 
>
>It is not that we care about events in different namespaces, it is
>that rdma, like everything else, doesn't care about namespaces and
>wants events from the netdev no matter where it is located.

Wait, so there is no notion of netnamespaces in rdma? I was under
impression rdma supports netnamespaces...


>
>Jason