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

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

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?

> 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.

> > 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.

> thanks,
> 
> greg k-h

Sebastian