linux-kernel - Re: [PATCH v2] drm/gma500: fix double freeing

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Message-ID: <CAMeQTsYon84hjPfhvsVXEGc6q9D0jsjXpaYyaMHY8ezAJWe=FQ@mail.gmail.com>
Date:	Wed, 7 Oct 2015 22:55:23 +0200
From:	Patrik Jakobsson <patrik.r.jakobsson@...il.com>
To:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:	David Airlie <airlied@...ux.ie>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v2] drm/gma500: fix double freeing

On Tue, Oct 6, 2015 at 5:48 PM, Sudip Mukherjee
<sudipm.mukherjee@...il.com> wrote:
> We are allocating backing using psbfb_alloc() and so
> backing->stolen is always true. So we were freeing backing two times.
> Moreover if we follow the execution path then we should be freeing
> backing after we have released the helper. So remove the one which frees
> backing before the helper is released.
> While at it the error labels are also renamed to give a meaningful
> name.
>
> Cc: Patrik Jakobsson <patrik.r.jakobsson@...il.com>
> Signed-off-by: Sudip Mukherjee <sudip@...torindia.org>
> ---
>
> Hi Patrik,
> If you donot like the labels I will change them according to what you
> have suggested.

Hi

Label names are used in all sorts of funny ways in the kernel. However
CodingStyle is quite clear on the matter: "Also don't name them after
the goto location like "err_kmalloc_failed:" and if you think about
it, it makes sense. Let's say we add another goto to that label then
the name wouldn't be correct anymore.

err_release and err_unlock would make me happier :)

With that fixed
Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@...il.com>

Thanks

>  drivers/gpu/drm/gma500/framebuffer.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/gma500/framebuffer.c b/drivers/gpu/drm/gma500/framebuffer.c
> index 2eaf1b3..52e2bf3 100644
> --- a/drivers/gpu/drm/gma500/framebuffer.c
> +++ b/drivers/gpu/drm/gma500/framebuffer.c
> @@ -411,7 +411,7 @@ static int psbfb_create(struct psb_fbdev *fbdev,
>         info = drm_fb_helper_alloc_fbi(&fbdev->psb_fb_helper);
>         if (IS_ERR(info)) {
>                 ret = PTR_ERR(info);
> -               goto out_err1;
> +               goto err_alloc_fbi;
>         }
>         info->par = fbdev;
>
> @@ -419,7 +419,7 @@ static int psbfb_create(struct psb_fbdev *fbdev,
>
>         ret = psb_framebuffer_init(dev, psbfb, &mode_cmd, backing);
>         if (ret)
> -               goto out_unref;
> +               goto err_framebuffer_init;
>
>         fb = &psbfb->base;
>         psbfb->fbdev = info;
> @@ -465,14 +465,9 @@ static int psbfb_create(struct psb_fbdev *fbdev,
>
>         mutex_unlock(&dev->struct_mutex);
>         return 0;
> -out_unref:
> -       if (backing->stolen)
> -               psb_gtt_free_range(dev, backing);
> -       else
> -               drm_gem_object_unreference(&backing->gem);
> -
> +err_framebuffer_init:
>         drm_fb_helper_release_fbi(&fbdev->psb_fb_helper);
> -out_err1:
> +err_alloc_fbi:
>         mutex_unlock(&dev->struct_mutex);
>         psb_gtt_free_range(dev, backing);
>         return ret;
> --
> 1.9.1
>
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