netdev - Re: [RFC 0/2] net: phy: Prevent an MDIO bus from being unloaded while in use

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Date:	Mon, 21 Jul 2014 11:42:38 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>
Subject: Re: [RFC 0/2] net: phy: Prevent an MDIO bus from being unloaded while
 in use

Hi Ezequiel,

2014-07-21 11:26 GMT-07:00 Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>:
> Hi all,
>
> This small patchset is a first proposal to fix the current lack of relationship
> between an ethernet driver and the MDIO bus behind the PHY device.
>
> In such cases, we would find no visible link between the drivers:
>
>   $ lsmod
>   Module                  Size  Used by    Not tainted
>   mvmdio                  2941  0
>   mvneta                 22069  0
>
> Which means nothing prevents the MDIO driver from being removed:
>
>   $ modprobe -r mvmdio
>
>   # Unable to handle kernel NULL pointer dereference at virtual address 00000060
>   pgd = c0004000
>   [00000060] *pgd=00000000
>   Internal error: Oops: 17 [#1] SMP ARM
>   Modules linked in: mvneta [last unloaded: mvmdio]
>   CPU: 0 PID: 22 Comm: kworker/0:1 Not tainted 3.16.0-rc5-01127-g62c0816-dirty #608
>   Workqueue: events_power_efficient phy_state_machine
>   task: df5ec840 ti: df67a000 task.ti: df67a000
>   PC is at phy_state_machine+0x1c/0x468
>   LR is at phy_state_machine+0x18/0x468
>   [snip]
>
> This patchset fixes this by calling module_{get,put} in the ethernet driver.
> After this patch, the mvmdio driver is no longer removable:
>
>   $ modprobe -r mvmdio
>   modprobe: can't unload module mvmdio: Resource temporarily unavailable
>
> Of course, we can expect a few drivers to have the same need and therefore
> we could argue about moving this to be part of the phydev connection.

Right, that's exactly what jumps to mind when I take a look at your
patch set. As long as a PHY device connected to a particular MDIO bus
is in used, we should make sure its refcount does not hit zero.

BTW, neither mvmdio nor mvneta seems to set their 'owner' field, is
that intentional?

>
> Ezequiel Garcia (2):
>   net: phy: Set the driver when registering an MDIO bus device
>   net: mvneta: Ensure the MDIO bus module is held
>
>  drivers/net/ethernet/marvell/mvneta.c | 12 ++++++++++++
>  drivers/net/phy/mdio_bus.c            |  1 +
>  2 files changed, 13 insertions(+)
>
> --
> 2.0.1
>



-- 
Florian
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