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

[Sumera Priyadarsini]

On Fri, 30 Oct, 2020, 1:32 PM Greg KH, <gregkh at linuxfoundation.org> wrote:

> 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 at 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.
>

Hi,

Sorry to jump in on the thread this way, but what exactly does a 'lifetime
managing proxy' for file operations mean? I am trying to understand how
DEFINE_DEBUGFS_ATTRIBUTE changes things wrt debug_ fs file operations but
can't find many resources. :(

Please let me know if I should be asking this in a different mailing
list/irc instead.

The change seems to be suggested by a coccinelle script.

Regards,
Sumera


thanks,
>
> greg k-h
>
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