Re: [PATCH 1/3] drm/i915: allocate mock file pointer dynamically

[Daniel Vetter]

On Mon, Mar 20, 2017 at 10:40:27AM +0100, Arnd Bergmann wrote:
> A struct file is a bit too large to put on the kernel stack in general
> and triggers a warning for low settings of CONFIG_FRAME_WARN:
> 
> drivers/gpu/drm/i915/selftests/mock_drm.c: In function 'mock_file':
> drivers/gpu/drm/i915/selftests/mock_drm.c:46:1: error: the frame size of 1328 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]
> drivers/gpu/drm/i915/selftests/mock_drm.c: In function 'mock_file_free':
> drivers/gpu/drm/i915/selftests/mock_drm.c:54:1: error: the frame size of 1312 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]
> 
> It's also slightly dangerous to leave a reference to a stack object
> in the drm_file structure after leaving the stack frame.
> This changes the code to just allocate the object dynamically
> and release it when we are done with it.
> 
> Fixes: 66d9cb5d805a ("drm/i915: Mock the GEM device for self-testing")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  drivers/gpu/drm/i915/selftests/mock_drm.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/selftests/mock_drm.c b/drivers/gpu/drm/i915/selftests/mock_drm.c
> index 113dec05c7dc..18514065c93d 100644
> --- a/drivers/gpu/drm/i915/selftests/mock_drm.c
> +++ b/drivers/gpu/drm/i915/selftests/mock_drm.c
> @@ -32,15 +32,15 @@ static inline struct inode fake_inode(struct drm_i915_private *i915)
>  struct drm_file *mock_file(struct drm_i915_private *i915)
>  {
>  	struct inode inode = fake_inode(i915);
> -	struct file filp = {};
> +	struct file *filp = kzalloc(sizeof(struct file), GFP_KERNEL);
>  	struct drm_file *file;
>  	int err;
>  
> -	err = drm_open(&inode, &filp);
> +	err = drm_open(&inode, filp);

Aside: We should have a FIXME and/or merge David Herrmanns code to allow a
drm_file without a real struct file for kernel-internal use ...
-Daniel

>  	if (unlikely(err))
>  		return ERR_PTR(err);
>  
> -	file = filp.private_data;
> +	file = filp->private_data;
>  	file->authenticated = true;
>  	return file;
>  }
> @@ -48,7 +48,9 @@ struct drm_file *mock_file(struct drm_i915_private *i915)
>  void mock_file_free(struct drm_i915_private *i915, struct drm_file *file)
>  {
>  	struct inode inode = fake_inode(i915);
> -	struct file filp = { .private_data = file };
> +	struct file *filp = file->filp;
>  
> -	drm_release(&inode, &filp);
> +	drm_release(&inode, filp);
> +
> +	kfree(filp);
>  }
> -- 
> 2.9.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch