netdev - Re: [PATCH v3 net-next 07/11] net: prep switchdev drivers for concurrent SWITCHDEV_ATTR_ID_PORT_BRIDGE

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Message-ID: <20210210102328.7jpzlobpwotdo63z@skbuf>
Date:   Wed, 10 Feb 2021 12:23:28 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        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>,
        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 v3 net-next 07/11] net: prep switchdev drivers for
 concurrent SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS

On Wed, Feb 10, 2021 at 12:12:57PM +0200, Ido Schimmel wrote:
> On Wed, Feb 10, 2021 at 11:14:41AM +0200, Vladimir Oltean wrote:
> > From: Vladimir Oltean <vladimir.oltean@....com>
> > 
> > Because the bridge will start offloading SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS
> > while not serialized by any lock such as the br->lock spinlock, existing
> > drivers that treat that attribute and cache the brport flags might no
> > longer work correctly.
> 
> Can you explain the race? This notification is sent from sysfs/netlink
> call path, both of which take rtnl.

Replying here to both you and Nikolay: there isn't any race, sorry, I
missed the fact that brport_store takes the rtnl_mutex and by extension
I thought that RTM_SETLINK runs unlocked too, without really checking.
Well, at least that's good news, the implementation can be a lot more
straightforward then...