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Date: Wed, 10 Feb 2021 12:45:49 +0200
From: Vladimir Oltean <olteanv@gmail.com>
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Subject: Re: [Bridge] [PATCH v3 net-next 00/11] Cleanup in brport flags
 switchdev offload for DSA
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To: Nikolay Aleksandrov <nikolay@nvidia.com>
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>, Ido Schimmel <idosch@idosch.org>, Claudiu Manoil <claudiu.manoil@nxp.com>, Grygorii Strashko <grygorii.strashko@ti.com>, Roopa Prabhu <roopa@nvidia.com>, Jakub Kicinski <kuba@kernel.org>, UNGLinuxDriver@microchip.com, "David S. Miller" <davem@davemloft.net>

Hi Nikolay,

On Wed, Feb 10, 2021 at 12:31:43PM +0200, Nikolay Aleksandrov wrote:
> Hi Vladimir,
> Let's take a step back for a moment and discuss the bridge unlock/lock sequences
> that come with this set. I'd really like to avoid those as they're a recipe
> for future problems. The only good way to achieve that currently is to keep
> the PRE_FLAGS call and do that in unsleepable context but move the FLAGS call
> after the flags have been changed (if they have changed obviously). That would
> make the code read much easier since we'll have all our lock/unlock sequences
> in the same code blocks and won't play games to get sleepable context.
> Please let's think and work in that direction, rather than having:
> +	spin_lock_bh(&p->br->lock);
> +	if (err) {
> +		netdev_err(p->dev, "%s\n", extack._msg);
> +		return err;
>  	}
> +
> 
> which immediately looks like a bug even though after some code checking we can
> verify it's ok. WDYT?
> 
> I plan to get rid of most of the br->lock since it's been abused for a very long
> time because it's essentially STP lock, but people have started using it for other
> things and I plan to fix that when I get more time.

This won't make the sysfs codepath any nicer, will it?