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

Byungchul Park
2017-03-01T05:27:36Z

On Tue, Feb 28, 2017 at 07:29:02PM +0100, Peter Zijlstra wrote:
> 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.

OK.

>
> 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.

Right. I decided to force MAX_XHLOCKS_NR to be power of 2 and everything
became easy. Thank you very much.