Quoting Dan Streetman (2018-09-27 20:41:21) > On Thu, Sep 27, 2018 at 4:27 PM Alex Xu (Hello71) <alex_y_xu@xxxxxxxx> wrote: > > > > Spinlocks are always lockable on UP systems, even if they were just > > locked. > > i think it would be much better to just use either > assert_spin_locked() or just spin_is_locked(), instead of an #ifdef. > I wrote a longer response and then learned about the WARN_ON_SMP macro, so I'll just use that instead. Original response below: I thought about using assert_spin_locked, but I wanted to keep the existing behavior, and it seems to make sense to try to lock the page if we forgot to lock it earlier? Maybe not though; I don't understand this code completely. I did write a version of z3fold_page_ensure_locked with "if (assert_spin_locked(...))" but not only did that look even worse, it doesn't even work, because assert_spin_locked is a statement on UP systems, not an expression. It might be worth adding a ensure_spin_locked function that does that though... spin_is_locked currently still always returns 0 "on CONFIG_SMP=n builds with CONFIG_DEBUG_SPINLOCK=n", so that would just return us to the same problem of checking CONFIG_SMP.
