On Mon, Oct 11, 2021 at 07:38:22PM +0300, Jani Nikula wrote: > On Mon, 11 Oct 2021, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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. Yes it does, it puts things at the root of debugfs. But why are you checking for NULL here, as the return value of a debugfs call can never be NULL? > However, since ->debugfs_root > comes from debugfs_create_dir() I presume it'll never be NULL on errors > anyway but rather an error pointer! That is correct. > So I think we probably need to go through the drm subsystem and look for > existing similar patterns in fix them. Please do. I know I made one pass at it a while ago but I think someone else went through and cleaned them up again. thanks, greg k-h
