Re: [PATCH] backing-dev: no need to check return value of debugfs_create functions

Greg Kroah-Hartman
2019-01-22T18:33:52Z

On Tue, Jan 22, 2019 at 06:19:08PM +0100, Sebastian Andrzej Siewior wrote:
> On 2019-01-22 17:25:03 [+0100], Greg Kroah-Hartman wrote:
> > > > }
> > > >
> > > > static void bdi_debug_unregister(struct backing_dev_info *bdi)
> > > > {
> > > > - debugfs_remove(bdi->debug_stats);
> > > > - debugfs_remove(bdi->debug_dir);
> > > > + debugfs_remove_recursive(bdi->debug_dir);
> > >
> > > this won't remove it.
> >
> > Which is fine, you don't care.
>
> but if you cat the stats file then it will dereference the bdi struct
> which has been free(), right?

Maybe, I don't know, your code is long gone, it doesn't matter :)

> > But step back, how could that original call be NULL? That only happens
> > if you pass it a bad parent dentry (which you didn't), or the system is
> > totally out of memory (in which case you don't care as everything else
> > is on fire).
>
> debugfs_get_inode() could do -ENOMEM and then the directory creation
> fails with NULL.

And if that happens, your system has worse problems :)

>
> > > If you return for "debug_dir == NULL" then it is a nice cleanup.
> >
> > No, that's not a valid thing to check for, you should not care as it
> > will not happen. And if it does happen, it's ok, it's only debugfs, no
> > one can rely on it, it is only for debugging.
>
> It might happen with ENOMEM as of now. It could happen for other reasons
> in future if the code changes.

As it's been that way for over a decade, I think we will be fine :)
If it changes in the future, in some way that actually matters, I'll go
back and fix up all of the callers.

thanks,

greg k-h