On Mon, Mar 25, 2019 at 02:23:15AM -0700, Ira Weiny wrote: > > > Unfortunately holding the lock is required to support FOLL_LONGTERM (to check > > > the VMAs) but we don't want to hold the lock to be optimal (specifically allow > > > FAULT_FOLL_ALLOW_RETRY). So I'm maintaining the optimization for *_fast users > > > who do not specify FOLL_LONGTERM. > > > > > > Another way to do this would have been to define __gup_longterm_unlocked with > > > the above logic, but that seemed overkill at this point. > > > > get_user_pages_unlocked() is an exported symbol, shouldn't it work > > with the FOLL_LONGTERM flag? > > > > I think it should even though we have no user.. > > > > Otherwise the GUP API just gets more confusing. > > I agree WRT to the API. But I think callers of get_user_pages_unlocked() are > not going to get the behavior they want if they specify FOLL_LONGTERM. Oh? Isn't the only thing FOLL_LONGTERM does is block the call on DAX? Why does the locking mode matter to this test? > What I could do is BUG_ON (or just WARN_ON) if unlocked is called with > FOLL_LONGTERM similar to the code in get_user_pages_locked() which does not > allow locked and vmas to be passed together: The GUP call should fail if you are doing something like this. But I'd rather not see confusing specialc cases in code without a clear comment explaining why it has to be there. Jason
