netdev - Re: [PATCH net-next 3/6] devlink: Count struct devlink consumers

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Message-ID: <20210816090700.313a54ba@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 16 Aug 2021 09:07:00 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Guangbin Huang <huangguangbin2@...wei.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Jiri Pirko <jiri@...dia.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Salil Mehta <salil.mehta@...wei.com>,
        Shannon Nelson <snelson@...sando.io>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        Yufeng Mo <moyufeng@...wei.com>
Subject: Re: [PATCH net-next 3/6] devlink: Count struct devlink consumers

On Mon, 16 Aug 2021 18:53:45 +0300 Leon Romanovsky wrote:
> On Mon, Aug 16, 2021 at 08:47:41AM -0700, Jakub Kicinski wrote:
> > On Sat, 14 Aug 2021 12:57:28 +0300 Leon Romanovsky wrote:  
> > > From: Leon Romanovsky <leonro@...dia.com>
> > > 
> > > The struct devlink itself is protected by internal lock and doesn't
> > > need global lock during operation. That global lock is used to protect
> > > addition/removal new devlink instances from the global list in use by
> > > all devlink consumers in the system.
> > > 
> > > The future conversion of linked list to be xarray will allow us to
> > > actually delete that lock, but first we need to count all struct devlink
> > > users.  
> > 
> > Not a problem with this set but to state the obvious the global devlink
> > lock also protects from concurrent execution of all the ops which don't
> > take the instance lock (DEVLINK_NL_FLAG_NO_LOCK). You most likely know
> > this but I thought I'd comment on an off chance it helps.  
> 
> The end goal will be something like that:
> 1. Delete devlink lock
> 2. Rely on xa_lock() while grabbing devlink instance (past devlink_try_get)
> 3. Convert devlink->lock to be read/write lock to make sure that we can run
> get query in parallel.
> 4. Open devlink netlink to parallel ops, ".parallel_ops = true".

IIUC that'd mean setting eswitch mode would hold write lock on 
the dl instance. What locks does e.g. registering a dl port take 
then?