On Tue, Jul 21, 2020 at 11:44:53AM -0700, Kees Cook wrote: > On Tue, Jul 21, 2020 at 11:51:04AM +0100, David Howells wrote: > > Kees Cook <[email protected]> wrote: > > > > > > Should mm->mm_users also be replaced by refcount_t? > > > > > > I'll say "yes". :) > > > https://lore.kernel.org/lkml/[email protected]/ > > > > > > > In addition, is it better to change all variables that use > > > > atomic_dec_and_test to control the release process to refconut_t? > > > > > > For the most part, yes. The following may find a lot of them: > > > scripts/coccinelle/api/atomic_as_refcounter.cocci > > > > I've been gradually undoing some of the conversions as there's no equivalent > > of atomic_add_return() and atomic_dec_return() that allow me to log the > > altered refcount through a tracepoint. > > Please do not _undo_ the changes; just add the API you need.
add_return and sub_return are horrible interface for refcount, which is the problem. If you meant: refcount_dec(), but want the old value for tracing, you want a different ordering than if you wanted to do refcount_dec_and_test(); dec_return can't know this. David, would something like a __refcount_*() API work where there is a 3rd argument (int *), which, if !NULL, will be assigned the old value?
