Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature

Peter Zijlstra
2017-02-28T18:31:49Z

On Tue, Feb 28, 2017 at 10:24:44PM +0900, Byungchul Park wrote:
> On Tue, Feb 28, 2017 at 02:10:12PM +0100, Peter Zijlstra wrote:

> > > +/* For easy access to xhlock */
> > > +#define xhlock(t, i) ((t)->xhlocks + (i))
> > > +#define xhlock_prev(t, l) xhlock(t, idx_prev((l) - (t)->xhlocks))
> > > +#define xhlock_curr(t) xhlock(t, idx(t))
> >
> > So these result in an xhlock pointer
> >
> > > +#define xhlock_incr(t) ({idx(t) = idx_next(idx(t));})
> >
> > This does not; which is confusing seeing how they share the same
> > namespace; also incr is weird.
>
> OK.. Could you suggest a better name? xhlock_adv()? advance_xhlock()?
> And.. replace it with a function?

How about doing: xhlocks_idx++ ? That is, keep all the indexes as
regular u32 and only reduce the space when using them as index.

Also, I would write the loop:

> +static int commit_xhlocks(struct cross_lock *xlock)
> +{
> + struct task_struct *curr = current;
> + struct hist_lock *xhlock_c = xhlock_curr(curr);
> + struct hist_lock *xhlock = xhlock_c;
> +
> + do {
> + xhlock = xhlock_prev(curr, xhlock);
> +
> + if (!xhlock_used(xhlock))
> + break;
> +
> + if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
> + break;
> +
> + if (same_context_xhlock(xhlock) &&
> + before(xhlock->prev_gen_id, xlock->hlock.gen_id) &&
> + !commit_xhlock(xlock, xhlock))
> + return 0;
> + } while (xhlock_c != xhlock);
> +
> + return 1;
> +}

like:

#define xhlock(i) current->xhlocks[i % MAX_XHLOCKS_NR]

for (i = 0; i < MAX_XHLOCKS_NR; i++) {
xhlock = xhlock(curr->xhlock_idx - i);

/* ... */
}

That avoids that horrible xhlock_prev() thing.