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

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Message-ID: <20210816084741.1dd1c415@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 16 Aug 2021 08:47:41 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Leon Romanovsky <leonro@...dia.com>,
        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 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 reference counting provides us a way to ensure that no new user
> space commands success to grab devlink instance which is going to be
> destroyed makes it is safe to access it without lock.