linux-kernel - Re: [PATCH 6/12] drivers/platform/x86: Correct redundant test

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Message-ID: <Pine.LNX.4.64.0907290422121.16543@ask.diku.dk>
Date:	Wed, 29 Jul 2009 04:22:51 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Jonathan Woithe <jwoithe@...sics.adelaide.edu.au>
Cc:	Paulo Marques <pmarques@...popie.com>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 6/12] drivers/platform/x86: Correct redundant test

On Wed, 29 Jul 2009, Jonathan Woithe wrote:

> Hi guys
> 
> > Julia Lawall wrote:
> > > [...]
> > > ---
> > >  drivers/platform/x86/fujitsu-laptop.c          |    3 ---
> > >  1 files changed, 0 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/platform/x86/fujitsu-laptop.c b/drivers/platform/x86/fujitsu-laptop.c
> > > index 218b9a1..5306901 100644
> > > --- a/drivers/platform/x86/fujitsu-laptop.c
> > > +++ b/drivers/platform/x86/fujitsu-laptop.c
> > > @@ -745,9 +745,6 @@ static int acpi_fujitsu_remove(struct acpi_device *device, int type)
> > >  
> > >  	fujitsu = acpi_driver_data(device);
> > >  
> > > -	if (!device || !acpi_driver_data(device))
> > > -		return -EINVAL;
> > > -
> > 
> > Shouldn't this still do a:
> > 
> >    if (!fujitsu)
> >      return -EINVAL;
> > 
> > to avoid dereferencing a NULL pointer below?
> 
> Hmm, yes it should.  Well spotted.  And I'm not certain how the duplicate
> test on "device" got in there in the first place.  I suspect it came about
> due to some structural changes made a few versions ago and I failed to
> notice that the second check became redundant.

If you are going to check fujitsu afterwards, then I think there is no 
need to test the result of acpi_driver_data before.

julia

 
> So, combining this with the above patch we should instead do
> 
> Signed-off-by: jwoithe@...sics.adelaide.edu.au <Jonathan Woithe>
> 
> --- a/drivers/platform/x86/fujitsu-laptop.c	2009-06-12 19:51:45.333234000 +0930
> +++ b/drivers/platform/x86/fujitsu-laptop.c	2009-07-29 10:14:30.610249941 +0930
> @@ -745,7 +745,7 @@ static int acpi_fujitsu_remove(struct ac
>  
>  	fujitsu = acpi_driver_data(device);
>  
> -	if (!device || !acpi_driver_data(device))
> +	if (!fujitsu)
>  		return -EINVAL;
>  
>  	fujitsu->acpi_handle = NULL;
> 
> Regards
>   jonathan
> --
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