On Mon, 11 Oct 2021, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > 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. Oh, thanks for the correction. > But why are you checking for NULL here, as the return value of a debugfs > call can never be NULL? Just musing on what is going on in the patch, and why such changes initially seem like good ideas and get through review. Thanks, Jani. > >> 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 -- Jani Nikula, Intel Open Source Graphics Center
