linux-kernel - Re: [PATCH v2 net-next 02/11] net: bridge: offload all port flags at once in br

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 9 Feb 2021 20:36:36 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bridge@...ts.linux-foundation.org, Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ido Schimmel <idosch@...sch.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com, Vadym Kochan <vkochan@...vell.com>,
        Taras Chornyi <tchornyi@...vell.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Ivan Vecera <ivecera@...hat.com>, linux-omap@...r.kernel.org
Subject: Re: [PATCH v2 net-next 02/11] net: bridge: offload all port flags at
 once in br_setport

On Tue, Feb 09, 2021 at 08:27:24PM +0200, Vladimir Oltean wrote:
> But there's an interesting side effect of allowing
> br_switchdev_set_port_flag to run concurrently (notifier call chains use
> a rw_semaphore and only take the read side). Basically now drivers that
> cache the brport flags in their entirety are broken, because there isn't
> any guarantee that bits outside the mask are valid any longer (we can
> even enforce that by masking the flags with the mask when notifying
> them). They would need to do the same trick of updating just the masked
> part of their cached flags. Except for the fact that they would need
> some sort of spinlock too, I don't think that the basic bitwise
> operations are atomic or anything like that. I'm a bit reluctant to add
> a spinlock in prestera, rocker, mlxsw just for this purpose. What do you
> think?

My take on things is that I can change those drivers to do what ocelot
and sja1105 do, which is to just have some bool values like this:

	if (flags.mask & BR_LEARNING)
		ocelot_port->learn_ena = !!(flags.val & BR_LEARNING);

which eliminates concurrency to the shared unsigned long brport_flags
variable. No locking, no complications.