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

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Date:   Mon, 20 Mar 2017 14:00:36 +0200
From:   Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Matthew Auld <matthew.auld@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] drm/i915: allocate mock file pointer dynamically

On ma, 2017-03-20 at 10:40 +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@...db.de>

<SNIP>

> ---
>  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;
>  

	filp = kzalloc(sizeof(*filp), GFP_KERNEL);
	if (unlikely(!filp)) {
		err = -ENOMEM;
		goto err;
	}

And appropriate onion teardown in case drm_open fails, so that we don't
leak memory.

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation