linux-kernel - Re: [PATCH 03/28] nvmem: add a notifier chain

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Date:   Wed, 8 Aug 2018 18:13:53 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Jonathan Corbet <corbet@....net>, Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Naren <naren.kernel@...il.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lukas Wunner <lukas@...ner.de>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Sven Van Asbroeck <svendev@...x.com>,
        Paolo Abeni <pabeni@...hat.com>, Alban Bedel <albeu@...e.fr>,
        Rob Herring <robh@...nel.org>,
        David Lechner <david@...hnology.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
        linux-mtd@...ts.infradead.org, linux-omap@...r.kernel.org,
        netdev@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 03/28] nvmem: add a notifier chain

On Wed, Aug 08, 2018 at 05:31:25PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> Add a blocking notifier chain with two events (add and remove) so that
> users can get notified about the addition of nvmem devices they're
> waiting for.
> 
> We'll use this instead of the at24 setup callback in the mityomapl138
> board file.

Hi Bartosz

What context is this notifier chain called in?

I did something similar using the i2c notifier to try to work around
the impending disappearing of the setup callback. But i got lockdep
splats, because the notifier was called while some locks were being
held, so it was not possible to register other i2c devices.

The at24 setup callback is done as part of probe, so no important
locks are held. Are any locks held when this notifier chain is called?

Thanks
	Andrew