linux-kernel - RE: [PATCH v6 05/14] platform/x86: dell-wmi-descriptor: split WMI descriptor into it's own driver

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Date:   Tue, 10 Oct 2017 13:40:04 +0000
From:   <Mario.Limonciello@...l.com>
To:     <pali.rohar@...il.com>
CC:     <dvhart@...radead.org>, <andy.shevchenko@...il.com>,
        <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <luto@...nel.org>,
        <quasisec@...gle.com>, <rjw@...ysocki.net>, <mjg59@...gle.com>,
        <hch@....de>, <greg@...ah.com>
Subject: RE: [PATCH v6 05/14] platform/x86: dell-wmi-descriptor: split WMI
 descriptor into it's own driver

> -----Original Message-----
> From: Pali Rohár [mailto:pali.rohar@...il.com]
> Sent: Tuesday, October 10, 2017 3:18 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; rjw@...ysocki.net;
> mjg59@...gle.com; hch@....de; Greg KH <greg@...ah.com>
> Subject: Re: [PATCH v6 05/14] platform/x86: dell-wmi-descriptor: split WMI
> descriptor into it's own driver
> 
> On Monday 09 October 2017 17:51:43 Mario Limonciello wrote:
> > +bool dell_wmi_get_interface_version(u32 *version)
> > +{
> > +	struct descriptor_priv *priv;
> > +
> > +	priv = list_first_entry_or_null(&wmi_list,
> > +					struct descriptor_priv,
> > +					list);
> > +	if (!priv)
> > +		return false;
> 
> This introduce race condition. In case callee of this function is
> executed before binding 8D9DDCBC-A997-11DA-B012-B622A1EF5492 WMI device
> into this dell-wmi-descriptor driver, then this function
> dell_wmi_get_interface_version() returns false. Even it is running on
> supported machine.
> 
> Loading of modulus and also binding devices to drivers (registered by
> modules) is is asynchronous.
> 

I suppose you're right, module dependency ordering doesn't necessarily
guarantee binding.  I'll add in some deferred probing and binding checking.

> In case everything is linked into vmlinux binary, this problem could
> happen too. Binding & initialization of WMI device to this driver can be
> postponed and callee (dell-wmi) would get false.

> 
> > +	*version = priv->interface_version;
> > +	return true;
> > +}
> > +EXPORT_SYMBOL_GPL(dell_wmi_get_interface_version);
> > +
> > +bool dell_wmi_get_size(u32 *size)
> > +{
> > +	struct descriptor_priv *priv;
> > +
> > +	priv = list_first_entry_or_null(&wmi_list,
> > +					struct descriptor_priv,
> > +					list);
> > +	if (!priv)
> > +		return false;
> 
> And same there.
> 
> > +	*size = priv->size;
> > +	return true;
> > +}
> > +EXPORT_SYMBOL_GPL(dell_wmi_get_size);
> 
> --
> Pali Rohár
> pali.rohar@...il.com