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

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Message-ID: <CAKMK7uHS837L9Ze_K5q-AsFgOtAMD+n_i_Y404BX-_CwJeP08Q@mail.gmail.com>
Date:   Tue, 21 May 2019 09:23:14 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Alex Deucher <alexdeucher@...il.com>
Cc:     "Pan, Xinhui" <Xinhui.Pan@....com>,
        "Zhou, David(ChunMing)" <David1.Zhou@....com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        xiaolinkui <xiaolinkui@...inos.cn>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Quan, Evan" <Evan.Quan@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>
Subject: Re: [PATCH] gpu: drm: use struct_size() in kmalloc()

On Tue, May 21, 2019 at 4:33 AM Alex Deucher <alexdeucher@...il.com> wrote:
>
> On Mon, May 20, 2019 at 7:19 PM Pan, Xinhui <Xinhui.Pan@....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/

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.

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

Cheers, Daniel

>
> Alex
>
> >
> >
> > 发件人: Daniel Vetter <daniel.vetter@...ll.ch> 代表 Daniel Vetter <daniel@...ll.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@...ux.ie; daniel@...ll.ch; Quan, Evan; xiaolinkui; amd-gfx@...ts.freedesktop.org; dri-devel@...ts.freedesktop.org; linux-kernel@...r.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@...ll.ch>
> >
> > Cheers, Daniel
> >
> > > From: xiaolinkui <xiaolinkui@...inos.cn>
> > > Sent: Friday, May 17, 2019 4:46:00 PM
> > > To: Deucher, Alexander; Koenig, Christian; Zhou, David(ChunMing); airlied@...ux.ie; daniel@...ll.ch; Pan, Xinhui; Quan, Evan
> > > Cc: amd-gfx@...ts.freedesktop.org; dri-devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org; xiaolinkui@...inos.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@...inos.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@...ts.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/amd-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

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