linux-kernel - Re: [PATCH 1/3] drivers/gpu/drm: Move a dereference below a NULL test

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Message-ID: <21d7e9970812191435g645c03ebqdcd53930d52f4830@mail.gmail.com>
Date:	Sat, 20 Dec 2008 08:35:19 +1000
From:	"Dave Airlie" <airlied@...il.com>
To:	"Julia Lawall" <julia@...u.dk>
Cc:	airlied@...ux.ie, dri-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/3] drivers/gpu/drm: Move a dereference below a NULL test

On Sat, Dec 20, 2008 at 3:10 AM, Julia Lawall <julia@...u.dk> wrote:
> From: Julia Lawall <julia@...u.dk>
>
> If the NULL test is necessary, then the dereference should be moved below
> the NULL test.
>
> The semantic patch that makes this change is as follows:
> (http://www.emn.fr/x-info/coccinelle/).  The result has been modified to
> move the initialization of driver down closer to where it is used.
>
> // <smpl>
> @@
> type T;
> expression E;
> identifier i,fld;
> statement S;
> @@
>
> - T i = E->fld;
> + T i;
>  ... when != E
>      when != i
>  if (E == NULL) S
> + i = E->fld;
> // </smpl>
>
> Signed-off-by: Julia Lawall <julia@...u.dk>
>
> ---
>  drivers/gpu/drm/drm_drv.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 0b9f316..4bdfc98 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -297,7 +297,7 @@ EXPORT_SYMBOL(drm_init);
>  */
>  static void drm_cleanup(struct drm_device * dev)
>  {
> -       struct drm_driver *driver = dev->driver;
> +       struct drm_driver *driver;
>
>        DRM_DEBUG("\n");
>
> @@ -324,8 +324,9 @@ static void drm_cleanup(struct drm_device * dev)
>                dev->agp = NULL;
>        }
>
> -       if (dev->driver->unload)
> -               dev->driver->unload(dev);
> +       driver = dev->driver;
> +       if (driver->unload)
> +               driver->unload(dev);

Huh?

The original test is to check it dev->driver->unload exists, not it
dev->driver exists.

I think your test  parameters are wrong.

Dave.

>
>        drm_ht_remove(&dev->map_hash);
>        drm_ctxbitmap_cleanup(dev);
> --
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