Re: [PATCH 1/3] drm/i915: allocate mock file pointer dynamically
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
> ---
> 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
Re: [PATCH 1/3] drm/i915: allocate mock file pointer dynamically
On Mon, Mar 20, 2017 at 1:00 PM, Joonas Lahtinen
wrote:
> On ma, 2017-03-20 at 10:40 +0100, Arnd Bergmann wrote:
>> 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.
Oops, of course you are right, sorry about that.
Arnd
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
> ---
> 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
Re: [PATCH 1/3] drm/i915: allocate mock file pointer dynamically
On Mon, Mar 20, 2017 at 1:02 PM, Arnd Bergmann wrote:
> On Mon, Mar 20, 2017 at 1:00 PM, Joonas Lahtinen
> wrote:
>> On ma, 2017-03-20 at 10:40 +0100, Arnd Bergmann wrote:
>
>>> 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.
>
> Oops, of course you are right, sorry about that.
Actually it's even worse, as I had originally planned to also allocate the inode
dynamically, but for some reasons didn't do that in the patch I sent.
This version of the patch as I sent it is rather bogus, so please ignore it
(but not the other two patches I sent). If David's solution to this problem
can make it into 4.12, there is no problem at all. Another alternative
would be to use anon_inode_getfile(), again with proper error handling
and cleanup. This is a bit slower but gives us valid file and inode structures.
Arnd
Re: [PATCH 1/3] drm/i915: allocate mock file pointer dynamically
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
> ---
> 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
>
> ___
> dri-devel mailing list
> dri-de...@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
