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);
> if (unlikely(err))
> return ERR_PTR(err);
>
> - file = filp.private_data;
> + file = filp->private_data;
What I don't like about this approach is that we leak the unwanted
inode/file. We only want the drm_file here and any access to above that
inside i915.ko is fubar.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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