netdev - Strangeness in ehea network driver's shutdown

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Message-ID: <20221001143131.6ondbff4r7ygokf2@pengutronix.de>
Date:   Sat, 1 Oct 2022 16:31:31 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Douglas Miller <dougmill@...ux.ibm.com>
Cc:     netdev@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>, kernel@...gutronix.de
Subject: Strangeness in ehea network driver's shutdown

Hello,

while doing some cleanup I stumbled over a problem in the ehea network
driver.

In the driver's probe function (ehea_probe_adapter() via
ehea_register_memory_hooks()) a reboot notifier is registered. When this
notifier is triggered (ehea_reboot_notifier()) it unregisters the
driver. I'm unsure what is the order of the actions triggered by that.
Maybe the driver is unregistered twice if there are two bound devices?
Or the reboot notifier is called under a lock and unregistering the
driver (and so the devices) tries to unregister the notifier that is
currently locked and so results in a deadlock? Maybe Greg or Rafael can
tell about the details here?

Whatever the effect is, it's strange. It makes me wonder why it's
necessary to free all the resources of the driver on reboot?! I don't
know anything about the specifics of the affected machines, but I guess
doing just the necessary stuff on reboot would be easier to understand,
quicker to execute and doesn't have such strange side effects.

With my lack of knowledge about the machine, the best I can do is report
my findings. So don't expect a patch or testing from my side.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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