linux-kernel - Re: [PATCH net-next 5/6] devlink: Reshuffle resource registration logic

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Date:   Fri, 19 Nov 2021 17:38:53 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>, Aya Levin <ayal@...lanox.com>,
        Claudiu Manoil <claudiu.manoil@....com>, drivers@...sando.io,
        Florian Fainelli <f.fainelli@...il.com>,
        Ido Schimmel <idosch@...dia.com>,
        intel-wired-lan@...ts.osuosl.org,
        Ioana Ciornei <ioana.ciornei@....com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Jiri Pirko <jiri@...dia.com>, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org,
        Michael Chan <michael.chan@...adcom.com>,
        netdev@...r.kernel.org, oss-drivers@...igine.com,
        Saeed Mahameed <saeedm@...dia.com>,
        Shannon Nelson <snelson@...sando.io>,
        Simon Horman <simon.horman@...igine.com>,
        Taras Chornyi <tchornyi@...vell.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        UNGLinuxDriver@...rochip.com,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next 5/6] devlink: Reshuffle resource registration
 logic

On Thu, Nov 18, 2021 at 05:48:13PM -0800, Jakub Kicinski wrote:
> On Thu, 18 Nov 2021 09:50:20 +0200 Leon Romanovsky wrote:
> > And it shouldn't. devlink_resource_find() will return valid resource only
> > if there driver is completely bogus with races or incorrect allocations of
> > resource_id.
> > 
> > devlink_*_register(..)
> >  mutex_lock(&devlink->lock);
> >  if (devlink_*_find(...)) {
> >     mutex_unlock(&devlink->lock);
> >     return ....;
> >  }
> >  .....
> > 
> > It is almost always wrong from locking and layering perspective the pattern above,
> > as it is racy by definition if not protected by top layer.
> > 
> > There are exceptions from the rule above, but devlink is clearly not the
> > one of such exceptions.
> 
> Just drop the unnecessary "cleanup" patches and limit the amount 
> of driver code we'll have to revert if your approach fails.

My approach works, exactly like it works in other subsystems.
https://lore.kernel.org/netdev/cover.1636390483.git.leonro@nvidia.com/

We are waiting to see your proposal extended to support parallel devlink
execution and to be applied to real drivers.
https://lore.kernel.org/netdev/20211030231254.2477599-1-kuba@kernel.org/

Anyway, you are maintainer, you want half work, you will get half work.

> 
> I spent enough time going back and forth with you.
> 
> Please.

Disagreements are hard for everyone, not only for you.

Thanks