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

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Oct 30, 2020 at 01:27:16PM +0530, Deepak R Varma wrote:
> 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@gmail.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.

Why do these drivers need these changes?  Are these files dynamically
removed from the system at random times?

There is a reason we didn't just do a global search/replace for this in
the kernel when the new functions were added, so I don't know why
checkpatch is now saying it must be done.

thanks,

greg k-h