Re: [Outreachy kernel] [PATCH] drm/amdgpu: use DEFINE_DEBUGFS_ATTRIBUTE with debugfs_create_file_unsafe()

[Christian König]

Am 30.10.20 um 08:57 schrieb Deepak R Varma:
> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.archive.carbon60.com%2Flinux%2Fkernel%2F2369498&data=04%7C01%7Cchristian.koenig%40amd.com%7Cddd7a6ac8164415a639708d87ca97004%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637396414464384011%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=o6GOHvMxNMuOPlC4nhDyURCHBLqfQZhYQq%2BiIMt3D3s%3D&reserved=0
> > >
> > > Issue reported by Coccinelle script:
> > > scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
> > >
> > > Signed-off-by: Deepak R Varma <mh12gx2825@xxxxxxxxx>
> > > ---
> > > 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.

Well since this is only created once per device instance I don't really 
care about this little overhead.

But what exactly is debugfs doing or not doing here?

Regards,
Christian.

> I will wait for comments from other experts for driver specific
> consideration / behavior.
>
> Thanks,
> drv
>
>
> > thanks,
> >
> > greg k-h