linux-kernel - Re: [PATCH 3/11] arch/x86/kernel: Correct NULL test

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Message-ID: <4e0ef1451002061407i6262b927l1eacfe2e5a3618c7@mail.gmail.com>
Date:	Sat, 6 Feb 2010 23:07:00 +0100
From:	Ludovic FERRE <ludovic.ferre@...il.com>
To:	Julia Lawall <julia@...u.dk>
Cc:	Joerg Roedel <joerg.roedel@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 3/11] arch/x86/kernel: Correct NULL test

Hello Julia,

May be it would be worthy to take your changes one step further and to
report if the function is called with a null device pointer (which
indicates a problem in the calling code, right?).

Here's a patch moving the null pointer check to its own if block and
reporting the null pointer function call using printk based on
2.6.33-rc6 code.

diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
index 23824fe..1a1d87c 100644
--- a/arch/x86/kernel/amd_iommu.c
+++ b/arch/x86/kernel/amd_iommu.c
@@ -114,11 +114,17 @@ static bool check_device(struct device *dev)
 {
       u16 devid;

-       if (!dev || !dev->dma_mask)
+       /* Function is called with a null pointer. Flag this and return false */
+       if (!dev){
+               printk(KERN_INFO "amd_iommu check_device called with a
null pointer device\n");
+               return false;
+       }
+
+       if (!dev->dma_mask)
               return false;

       /* No device or no PCI device */
-       if (!dev || dev->bus != &pci_bus_type)
+       if (dev->bus != &pci_bus_type)
               return false;

       devid = get_device_id(dev);

On Sat, Feb 6, 2010 at 9:42 AM, Julia Lawall <julia@...u.dk> wrote:
> From: Julia Lawall <julia@...u.dk>
>
> dev was tested just above, so drop the second test.
>
> A simplified version of the semantic match that finds this problem is as
> follows: (http://coccinelle.lip6.fr/)
>
> // <smpl>
> @r@
> expression *x;
> expression e;
> identifier l;
> @@
>
> if (x == NULL || ...) {
>    ... when forall
>    return ...; }
> ... when != goto l;
>    when != x = e
>    when != &x
> *x == NULL
> // </smpl>
>
> Signed-off-by: Julia Lawall <julia@...u.dk>
>
> ---
>  arch/x86/kernel/amd_iommu.c         |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
> index adb0ba0..2c4a501 100644
> --- a/arch/x86/kernel/amd_iommu.c
> +++ b/arch/x86/kernel/amd_iommu.c
> @@ -118,7 +118,7 @@ static bool check_device(struct device *dev)
>                return false;
>
>        /* No device or no PCI device */
> -       if (!dev || dev->bus != &pci_bus_type)
> +       if (dev->bus != &pci_bus_type)
>                return false;
>
>        devid = get_device_id(dev);
> --
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-- 
Ludovic
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