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Message-ID: <20170524122413.702e0eef@cakuba.netronome.com> Date: Wed, 24 May 2017 12:24:13 -0700 From: Jakub Kicinski <kubakici@...pl> To: Jiri Pirko <jiri@...nulli.us> Cc: netdev@...r.kernel.org, oss-drivers@...ronome.com Subject: Re: [PATCH net-next 2/4] nfp: register ports as devlink ports On Wed, 24 May 2017 14:35:14 +0200, Jiri Pirko wrote: > >+void nfp_devlink_port_unregister(struct nfp_port *port) > >+{ > >+ /* Due to unpleasant lock ordering we may see the port go away before > >+ * we have fully probed. > > Could you elaborate on this a bit more please? It's partially due to peculiarities of the management FW more than kernel stuff. Unfortunately some ethtool media config requires reboot to be applied, so we print a friendly message to the logs and unregister the associated netdevs. Which means once netdevs get registered ports may go away. Enter devlink, I need the ability to grab the adapater lock in split/unsplit callbacks to find the ports, which implies having to drop that lock before I register devlink. And only after I register devlink can I register the ports. I could do init without registering anything, drop the adapter lock, register devlink, and then grab the adapter lock back and register devlink ports and netdevs. But there is another issue... Since I look for ports on a list maintained in the adapter struct, driver code doesn't care if devlink_port has been registered or not. The moment devlink is registered, split/unsplit requests will be accepted - potentially trying to unregister devlink_port before the register could happen. Further down the line, also, the eswitch mode setting is coming. Which means the moment I register devlink itself ports will get shuffled (due to the plan of registering VFs as ports :)). I feel like registering devlink should be the last action of the driver, really. My plan was to keep that simple if() for now, and once we get to extending devlink with SR-IOV stuff also add the ability to pre-register ports. Allow registering ports on not-yet-registered devlink (probably put them on a private list within struct devlink). This would make devlink_register() a single point when everything devlink becomes visible, atomically, instead of devlink itself coming first and then ports following. Does that make sense? Am I misreading the code (again :S)?
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