netdev - Re: [PATCH net] net: phy: Fix lack of reference count on PHY driver

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Message-ID: <20170203095427.GA27312@n2100.armlinux.org.uk>
Date:   Fri, 3 Feb 2017 09:54:27 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     David Miller <davem@...emloft.net>
Cc:     f.fainelli@...il.com, netdev@...r.kernel.org, andrew@...n.ch,
        maowenan@...wei.com
Subject: Re: [PATCH net] net: phy: Fix lack of reference count on PHY driver

On Thu, Feb 02, 2017 at 09:54:07PM -0500, David Miller wrote:
> Hot plugging PHYs and notifications and all of that business is
> net-next material.

I was talking more about unbinding of the driver, which is something
that can be done today, eg:

$ ls -l /sys/bus/mdio_bus/drivers/Atheros\ 8035\ ethernet/
total 0
lrwxrwxrwx 1 root root    0 Feb  3 09:49 2188000.ethernet:00 -> ../../../../devices/soc0/soc/2100000.aips-bus/2188000.ethernet/mdio_bus/2188000.ethernet/2188000.ethernet:00
--w------- 1 root root 4096 Feb  3 09:49 bind
--w------- 1 root root 4096 Feb  3 09:49 uevent
--w------- 1 root root 4096 Feb  3 09:49 unbind
$ echo 2188000.ethernet:00 > /sys/bus/mdio_bus/drivers/Atheros\ 8035\ ethernet/unbind

is all it takes, and the same oops will happen.  Try it on a box
you don't care about crashing. :)

This is my point - locking the module into the kernel using
try_module_get() doesn't actually fix the problem where drivers are
concerned, it just has the illusion of being safe.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.