linux-kernel - Re: [Outreachy kernel] [PATCH] drm/amdgpu: use DEFINE_DEBUGFS_ATTRIBUTE with debugfs_create_file

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Date:   Fri, 30 Oct 2020 13:27:16 +0530
From:   Deepak R Varma <mh12gx2825@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     outreachy-kernel@...glegroups.com,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        melissa.srw@...il.com, daniel.vetter@...ll.ch, mh12gx2825@...il.com
Subject: Re: [Outreachy kernel] [PATCH] drm/amdgpu: use
 DEFINE_DEBUGFS_ATTRIBUTE with debugfs_create_file_unsafe()

On Fri, Oct 30, 2020 at 08:11:20AM +0100, Greg KH wrote:
> On Fri, Oct 30, 2020 at 08:52:45AM +0530, Deepak R Varma wrote:
> > Using DEFINE_DEBUGFS_ATTRIBUTE macro with debugfs_create_file_unsafe()
> > function in place of the debugfs_create_file() function will make the
> > file operation struct "reset" aware of the file's lifetime. Additional
> > details here: https://lists.archive.carbon60.com/linux/kernel/2369498
> > 
> > Issue reported by Coccinelle script:
> > scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
> > 
> > Signed-off-by: Deepak R Varma <mh12gx2825@...il.com>
> > ---
> > Please Note: This is a Outreachy project task patch.
> > 
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 20 ++++++++++----------
> >  1 file changed, 10 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> > index 2d125b8b15ee..f076b1ba7319 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> > @@ -1551,29 +1551,29 @@ static int amdgpu_debugfs_sclk_set(void *data, u64 val)
> >  	return 0;
> >  }
> >  
> > -DEFINE_SIMPLE_ATTRIBUTE(fops_ib_preempt, NULL,
> > -			amdgpu_debugfs_ib_preempt, "%llu\n");
> > +DEFINE_DEBUGFS_ATTRIBUTE(fops_ib_preempt, NULL,
> > +			 amdgpu_debugfs_ib_preempt, "%llu\n");
> 
> Are you sure this is ok?  Do these devices need this additional
> "protection"?  Do they have the problem that these macros were written
> for?
> 
> Same for the other patches you just submitted here, I think you need to
> somehow "prove" that these changes are necessary, checkpatch isn't able
> to determine this all the time.

Hi Greg,
Based on my understanding, the current function debugfs_create_file()
adds an overhead of lifetime managing proxy for such fop structs. This
should be applicable to these set of drivers as well. Hence I think this
change will be useful.

I will wait for comments from other experts for driver specific
consideration / behavior.

Thanks,
drv


> 
> thanks,
> 
> greg k-h