linux-kernel - RE: [PATCH] platform/x86: dell-*wmi*: Relay failed initial probe to dependent drivers

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Message-ID: <8a19372f91e34d96ab16e8d4c31b0c86@ausx13mpc124.AMER.DELL.COM>
Date:   Fri, 3 Nov 2017 14:42:55 +0000
From:   <Mario.Limonciello@...l.com>
To:     <dvhart@...radead.org>
CC:     <andy.shevchenko@...il.com>, <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <pali.rohar@...il.com>
Subject: RE: [PATCH] platform/x86: dell-*wmi*: Relay failed initial probe to
 dependent drivers

> -----Original Message-----
> From: Darren Hart [mailto:dvhart@...radead.org]
> Sent: Thursday, November 2, 2017 7:57 PM
> To: Limonciello, Mario <Mario_Limonciello@...l.com>
> Cc: Andy Shevchenko <andy.shevchenko@...il.com>; LKML <linux-
> kernel@...r.kernel.org>; platform-driver-x86@...r.kernel.org;
> pali.rohar@...il.com
> Subject: Re: [PATCH] platform/x86: dell-*wmi*: Relay failed initial probe to
> dependent drivers
> 
> On Wed, Nov 01, 2017 at 02:28:21PM -0500, Mario Limonciello wrote:
> > dell-wmi and dell-smbios-wmi are dependent upon dell-wmi-descriptor
> > finishing probe successfully to probe themselves.
> >
> > Currently if dell-wmi-descriptor fails probing in a non-recoverable way
> > (such as invalid header) dell-wmi and dell-smbios-wmi will continue to
> > try to redo probing due to deferred probing.
> >
> > To solve this have the dependent drivers query the dell-wmi-descriptor
> > driver whether the descriptor has been determined valid. The possible
> > results are:
> > -EPROBE_DEFER: Descriptor not yet probed, dependent driver should wait
> >  and use deferred probing
> > < 0: Descriptor probed, invalid.  Dependent driver should return an
> >  error.
> > 0: Successful descriptor probe, dependent driver can continue
> >
> > Successful descriptor probe still doesn't mean that the descriptor driver
> > is necessarily bound at the time of initialization of dependent driver.
> > Userspace can unbind the driver, so all methods used from driver
> > should still be verified to return success values otherwise deferred
> > probing be used.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@...l.com>
> 
> > diff --git a/drivers/platform/x86/dell-wmi-descriptor.c
> b/drivers/platform/x86/dell-wmi-descriptor.c
> > index 3204c408e261..33c6c7d66f8c 100644
> > --- a/drivers/platform/x86/dell-wmi-descriptor.c
> > +++ b/drivers/platform/x86/dell-wmi-descriptor.c
> > @@ -26,9 +26,16 @@ struct descriptor_priv {
> >  	u32 interface_version;
> >  	u32 size;
> >  };
> > +static int descriptor_valid;
> 
> This initializes to 0, which I believe creates an odd race window between when
> this init is called and when the first driver calls
> dell_wmi_get_descriptor_valid(). Seems like initializing to -EPROBE_DEFER here
> in the declaration would be a better right approach.
> 
> --

Thanks, good catch.  I'll adjust.