[Intel-gfx] [PATCH v2 3/3] drm: Protect fb_helper list manipulation with a mutex

[Sean Paul]

On Tue, Nov 29, 2016 at 7:02 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> Though we only walk the kernel_fb_helper_list inside a panic (or single
> thread debugging), we still need to protect the list manipulation on
> creating/removing a framebuffer device in order to prevent list
> corruption.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Reviewed-by: Sean Paul <seanpaul at chromium.org>

> ---
>  drivers/gpu/drm/drm_fb_helper.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 90da28d2fcf3..e934b541feea 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -49,6 +49,7 @@ MODULE_PARM_DESC(fbdev_emulation,
>                  "Enable legacy fbdev emulation [default=true]");
>
>  static LIST_HEAD(kernel_fb_helper_list);
> +static DEFINE_MUTEX(kernel_fb_helper_lock);
>
>  /**
>   * DOC: fbdev helpers
> @@ -855,12 +856,14 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
>         if (!drm_fbdev_emulation)
>                 return;
>
> +       mutex_lock(&kernel_fb_helper_lock);
>         if (!list_empty(&fb_helper->kernel_fb_list)) {
>                 list_del(&fb_helper->kernel_fb_list);
>                 if (list_empty(&kernel_fb_helper_list)) {
>                         unregister_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
>                 }
>         }
> +       mutex_unlock(&kernel_fb_helper_lock);
>
>         drm_fb_helper_crtc_free(fb_helper);
>
> @@ -2258,10 +2261,12 @@ int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel)
>         dev_info(dev->dev, "fb%d: %s frame buffer device\n",
>                  info->node, info->fix.id);
>
> +       mutex_lock(&kernel_fb_helper_lock);
>         if (list_empty(&kernel_fb_helper_list))
>                 register_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
>
>         list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list);
> +       mutex_unlock(&kernel_fb_helper_lock);
>
>         return 0;
>  }
> --
> 2.10.2
>
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