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Date: Wed, 10 Feb 2021 12:23:28 +0200
From: Vladimir Oltean <olteanv@gmail.com>
Message-ID: <20210210102328.7jpzlobpwotdo63z@skbuf>
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 <20210210101257.GA287766@shredder.lan>
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Subject: Re: [Bridge] [PATCH v3 net-next 07/11] net: prep switchdev drivers
 for concurrent SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS
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To: Ido Schimmel <idosch@idosch.org>
Cc: Ivan Vecera <ivecera@redhat.com>, Andrew Lunn <andrew@lunn.ch>, Alexandre Belloni <alexandre.belloni@bootlin.com>, Florian Fainelli <f.fainelli@gmail.com>, Jiri Pirko <jiri@resnulli.us>, Vadym Kochan <vkochan@marvell.com>, linux-omap@vger.kernel.org, netdev@vger.kernel.org, bridge@lists.linux-foundation.org, Ioana Ciornei <ioana.ciornei@nxp.com>, linux-kernel@vger.kernel.org, Vivien Didelot <vivien.didelot@gmail.com>, Taras Chornyi <tchornyi@marvell.com>, Claudiu Manoil <claudiu.manoil@nxp.com>, Grygorii Strashko <grygorii.strashko@ti.com>, Nikolay Aleksandrov <nikolay@nvidia.com>, Roopa Prabhu <roopa@nvidia.com>, Jakub Kicinski <kuba@kernel.org>, UNGLinuxDriver@microchip.com, "David S. Miller" <davem@davemloft.net>

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@nxp.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...