linux-kernel - Re: [PATCH v10 13/15] platform/x86: wmi: create userspace interface for drivers

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Date:   Fri, 20 Oct 2017 16:48:39 +0200
From:   Christoph Hellwig <hch@....de>
To:     Mario.Limonciello@...l.com
Cc:     greg@...ah.com, dvhart@...radead.org, andy.shevchenko@...il.com,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        luto@...nel.org, quasisec@...gle.com, pali.rohar@...il.com,
        rjw@...ysocki.net, mjg59@...gle.com, hch@....de,
        gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH v10 13/15] platform/x86: wmi: create userspace
        interface for drivers

On Fri, Oct 20, 2017 at 01:54:36PM +0000, Mario.Limonciello@...l.com wrote:
> > -----Original Message-----
> > From: Greg KH [mailto:greg@...ah.com]
> > Sent: Friday, October 20, 2017 8:22 AM
> > To: Limonciello, Mario <Mario_Limonciello@...l.com>
> > Cc: dvhart@...radead.org; Andy Shevchenko <andy.shevchenko@...il.com>;
> > LKML <linux-kernel@...r.kernel.org>; platform-driver-x86@...r.kernel.org; Andy
> > Lutomirski <luto@...nel.org>; quasisec@...gle.com; pali.rohar@...il.com;
> > rjw@...ysocki.net; mjg59@...gle.com; hch@....de; Alan Cox
> > <gnomes@...rguk.ukuu.org.uk>
> > Subject: Re: [PATCH v10 13/15] platform/x86: wmi: create userspace interface for
> > drivers
> > 
> > On Thu, Oct 19, 2017 at 12:50:16PM -0500, Mario Limonciello wrote:
> > > +	wblock = container_of(wdev, struct wmi_block, dev);
> > > +	if (!wblock)
> > > +		return -ENODEV;
> > 
> > How can container_of() ever return NULL?  If so, you have a very odd
> > memory layout...
> > 
> 
> I'm assuming this is from set_required_buffer_size right?
> 
> The symbol is exported out for other drivers to use.  It's possible for another
> driver to allocate a wmi_device structure that's not part of a wblock.

container_of can never return NULL, it does arithmetics on a pointer
based on the type it is embedded into.

You better don't register a wmi_device that's not part of the block
with your driver.  Which others drivers are those, btw?

> > > +	list_for_each_entry_safe(wblock, next, &wmi_block_list, list) {
> > > +		wdriver = container_of(wblock->dev.dev.driver,
> > > +					struct wmi_driver, driver);
> > > +		if (!wdriver)
> > > +			continue;
> > 
> > Same here.  And other places in this file.
> > 
> 
> This one it's possible that a driver isn't bound to a device, and when
> that happens wdriver is NULL.

See above, no it can't.  Maybe wblock->dev.dev.driver can be NULL,
but in that case you must not call container_of on it.