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

From: Jiri Pirko
Date: Tue Nov 16 2021 - 01:57:35 EST

Mon, Nov 15, 2021 at 04:09:31PM CET, jgg@xxxxxxxxxx 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.
>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...