Re: [PATCH] gpu: drm: use struct_size() in kmalloc()

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 21.05.19 um 09:23 schrieb Daniel Vetter:
> On Tue, May 21, 2019 at 4:33 AM Alex Deucher <alexdeucher@gmail.com> wrote:
>> On Mon, May 20, 2019 at 7:19 PM Pan, Xinhui <Xinhui.Pan@amd.com> wrote:
>>> Daniel, what you are talking about is totally wrong.
>>> 1) AFAIK, only one zero-size array can be in the end of a struct.
>>> 2) two struct_size will add up struct itself twice. the sum is wrong then.
>>>
>>> No offense. I can't help feeling lucky that you are in intel.
>> Xinhui,
>>
>> Please keep things civil.  There is no need for comments like this.
> Yeah, this was over the line, thanks Alex for already taking care of
> this. Please note that fd.o mailing lists operate under a CoC:
>
> https://www.freedesktop.org/wiki/CodeOfConduct/

Seconded. I also enjoy the humiliation of other in email, but it doesn't 
helps us getting code written and problems solved in a professional 
environment.

> Wrt the technical comment: I know that you can only do one variable
> sized array, and it must be at the end. But you can put multiple
> structures all within the same allocation. Which is what I thought you
> wanted to do. And my sketch would allow you to do that even if you
> have multiple variable length structures you want to allocate. There's
> plenty examples of this (but open-coded ones) in the kernel.

BTW: Is there actually good documentation how to correctly do the 
variable length array at end of structure thing in the kernel?

I do know that I've seen a lot of different variants like array[] 
array[0] or array[1] and I have also seen a bunch of gcc versions 
failing to generate correct code for some of them.

So we should probably nail down how to do things correctly.

> Except in really hot paths I personally think that that kind of
> trickery isn't worth it.

Well for kmalloc() it's not that much overhead, but with vmalloc that is 
a completely different picture.

Christian.

>
> Cheers, Daniel
>
>> Alex
>>
>>>
>>> 发件人: Daniel Vetter <daniel.vetter@ffwll.ch> 代表 Daniel Vetter <daniel@ffwll.ch>
>>> 发送时间: 2019年5月21日 0:28
>>> 收件人: Pan, Xinhui
>>> 抄送: Deucher, Alexander; Koenig, Christian; Zhou, David(ChunMing); airlied@linux.ie; daniel@ffwll.ch; Quan, Evan; xiaolinkui; amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org
>>> 主题: Re: [PATCH] gpu: drm: use struct_size() in kmalloc()
>>>
>>> [CAUTION: External Email]
>>>
>>> On Fri, May 17, 2019 at 04:44:30PM +0000, Pan, Xinhui wrote:
>>>> I am going to put more members which are also array after this struct,
>>>> not only obj[].  Looks like this struct_size did not help on multiple
>>>> array case. Thanks anyway.  ________________________________
>>> You can then add them up, e.g. kmalloc(struct_size()+struct_size(),
>>> GFP_KERNEL), so this patch here still looks like a good idea.
>>>
>>> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>>>
>>> Cheers, Daniel
>>>
>>>> From: xiaolinkui <xiaolinkui@kylinos.cn>
>>>> Sent: Friday, May 17, 2019 4:46:00 PM
>>>> To: Deucher, Alexander; Koenig, Christian; Zhou, David(ChunMing); airlied@linux.ie; daniel@ffwll.ch; Pan, Xinhui; Quan, Evan
>>>> Cc: amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org; xiaolinkui@kylinos.cn
>>>> Subject: [PATCH] gpu: drm: use struct_size() in kmalloc()
>>>>
>>>> [CAUTION: External Email]
>>>>
>>>> Use struct_size() helper to keep code simple.
>>>>
>>>> Signed-off-by: xiaolinkui <xiaolinkui@kylinos.cn>
>>>> ---
>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c | 3 +--
>>>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c
>>>> index 22bd21e..4717a64 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c
>>>> @@ -1375,8 +1375,7 @@ int amdgpu_ras_init(struct amdgpu_device *adev)
>>>>          if (con)
>>>>                  return 0;
>>>>
>>>> -       con = kmalloc(sizeof(struct amdgpu_ras) +
>>>> -                       sizeof(struct ras_manager) * AMDGPU_RAS_BLOCK_COUNT,
>>>> +       con = kmalloc(struct_size(con, objs, AMDGPU_RAS_BLOCK_COUNT),
>>>>                          GFP_KERNEL|__GFP_ZERO);
>>>>          if (!con)
>>>>                  return -ENOMEM;
>>>> --
>>>> 2.7.4
>>>>
>>>>
>>>>
>>> --
>>> Daniel Vetter
>>> Software Engineer, Intel Corporation
>>> http://blog.ffwll.ch
>>> _______________________________________________
>>> amd-gfx mailing list
>>> amd-gfx@lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
>
>