Re: Fw: [Intel-gfx] [PATCH 1/5] dri: cleanup debugfs error handling

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 11 Oct 2021, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Mon, Oct 11, 2021 at 04:19:58PM +0200, Christian König wrote:
>> > > > > And then throw it away, later, when you want to remove the directory,
>> > > > > look it up with a call to debugfs_lookup() and pass that to
>> > > > > debugfs_remove() (which does so recursively).
>> > > > > 
>> > > > > There should never be a need to save, or check, the result of any
>> > > > > debugfs call.  If so, odds are it is being used incorrectly.
>> > > Yeah, exactly that's the problem I see here.
>> > > 
>> > > We save the return value because the DRM subsystem is creating a debugfs
>> > > directory for the drivers to use.
>> > That's fine for now, not a big deal.  And even if there is an error,
>> > again, you can always feed that error back into the debugfs subsystem on
>> > another call and it will handle it correctly.
>> 
>> Problem is it isn't, we have a crash because the member isn't a pointer but
>> an ERR_PTR instead.
>
> Again, that is fine, you can feed that into debugfs and it will "just
> work".  Treat it as an opaque pointer, not a *dentry and you will be
> fine.

Hmm, some of the patches add things like:

+
+	if (!root)
+		goto error;
+
	minor->debugfs_root = debugfs_create_dir(name, root);

Superficially this seems okay, as it looks like debugfs_create_dir()
doesn't actually cope with NULL values. However, since ->debugfs_root
comes from debugfs_create_dir() I presume it'll never be NULL on errors
anyway but rather an error pointer!

So I think we probably need to go through the drm subsystem and look for
existing similar patterns in fix them.

BR,
Jani.



>
> thanks,
>
> greg k-h

-- 
Jani Nikula, Intel Open Source Graphics Center