On Fri, May 31, 2019 at 03:20:12PM +0100, David Howells wrote: > Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > (and it has already been established that refcount_t doesn't work for > > usage count scenarios) > > ? > > Does that mean struct kref doesn't either? Indeed, since kref is just a pointless wrapper around refcount_t it does not either. The main distinction between a reference count and a usage count is that 0 means different things. For a refcount 0 means dead. For a usage count 0 is merely unused but valid. Incrementing a 0 refcount is a serious bug -- use-after-free (and hence refcount_t will refuse this and splat), for a usage count this is no problem. Now, it is sort-of possible to merge the two, by basically stating something like: usage = refcount - 1. But that can get tricky and people have not really liked the result much for the few times I tried.
