linux-kernel - Re: [PATCH v2] uio: ensure class is registered before devices

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Message-ID: <20180816103450.GF21707@piout.net>
Date:   Thu, 16 Aug 2018 12:34:50 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] uio: ensure class is registered before devices

On 16/08/2018 12:04:13+0200, Greg Kroah-Hartman wrote:
> On Thu, Aug 16, 2018 at 10:34:38AM +0200, Alexandre Belloni wrote:
> > On 16/08/2018 10:01:12+0200, Greg Kroah-Hartman wrote:
> > > On Thu, Aug 16, 2018 at 09:39:41AM +0200, Alexandre Belloni wrote:
> > > > When both uio and the uio drivers are built in the kernel, it is possible
> > > > for a driver to register devices before the uio class is registered.
> > > 
> > > How does this happen?  The link order should solve this issue, right?
> > > 
> > 
> > Sure, if we can ensure uio_init() is called before any driver calls
> > uio_register_device() then this would not happen. However, I'm not sure
> > how you would want to achieve that.
> 
> That is the job of the link order, does this not work properly today?
> How have you triggered this so that you could test your patch?
> 

I have a (not yet upstreamed) MFD driver in drivers/mfd that is
registering the uio device. It mostly look like uio_pci_generic.c.

When compiling both as builtin, it will crash that way.

There are no link dependency between uio_init and uio_register_device
calls so I guess the linker can't reorder that properly.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com