netdev - Re: [PATCH v2 net-next 2/7] net: dsa: merge all bools of struct dsa

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Date:   Wed, 5 Jan 2022 10:46:44 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>
Subject: Re: [PATCH v2 net-next 2/7] net: dsa: merge all bools of struct
 dsa_port into a single u8

On 1/5/22 10:39 AM, Vladimir Oltean wrote:
> Hi Florian,
> 
> On Wed, Jan 05, 2022 at 10:30:54AM -0800, Florian Fainelli wrote:
>> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
> 
> Thanks a lot for the review.
> 
> I'm a bit on the fence on this patch and the other one for dsa_switch.
> The thing is that bit fields are not atomic in C89, so if we update any
> of the flags inside dp or ds concurrently (like dp->vlan_filtering),
> we're in trouble. Right now this isn't a problem, because most of the
> flags are set either during probe, or during ds->ops->setup, or are
> serialized by the rtnl_mutex in ways that are there to stay (switchdev
> notifiers). That's why I didn't say anything about it. But it may be a
> caveat to watch out for in the future. Do you think we need to do
> something about it? A lock would not be necessary, strictly speaking.

I would probably start with a comment that describes these pitfalls, I
wish we had a programmatic way to ensure that these flags would not be
set dynamically and outside of the probe/setup path but that won't
happen easily.

Should we be switching to a bitmask and bitmap helpers to be future proof?
-- 
Florian