netdev - Re: [PATCH net-next 2/9] net: devlink: remove region snapshots list dependency on devlink->lock

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Date:   Thu, 28 Jul 2022 09:16:45 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Moshe Shemesh <moshe@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Tariq Toukan <tariqt@...dia.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Jiri Pirko <jiri@...dia.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/9] net: devlink: remove region snapshots list
 dependency on devlink->lock

On Thu, 28 Jul 2022 10:50:29 +0200 Jiri Pirko wrote:
> >> So resolve this by removing dependency on devlink->lock for region
> >> snapshots list consistency and introduce new mutex to ensure it.  
> >
> >I was hoping to avoid per-subobject locks. What prevents us from
> >depending on the instance lock here (once the driver is converted)?  
> 
> The fact that it could be called in mlx4 from both devl locked and
> unlocked context. Basically whenever CMD to fw is called.

Ok, I guess mlx4 uses regions as proto-health reporters so too hard of
a battle to fight. Please update the commit message tho.

> What is wrong in small locks here and there when they are sufficient?

The more locks the less obvious the semantics and ordering of locking
are.