Messages in this thread | | | Subject | Re: [PATCH 1/3] rhashtable: further improve stability of rhashtable_walk | From | Paolo Abeni <> | Date | Fri, 06 Jul 2018 12:12:20 +0200 |
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On Fri, 2018-07-06 at 19:55 +1000, NeilBrown wrote: > On Fri, Jul 06 2018, Paolo Abeni wrote: > > > Note: the code under test is a pending new patch I'm holding due to the > > above issue, I can send it as RFC to share the code if you think it may > > help. > > I'd suggest post it. I may not get a chance to look at it, but if you > don't post it, then I definitely won't :-)
Oks, thanks, I just spammed the list (and you ;)
> > > @@ -867,15 +866,39 @@ void *rhashtable_walk_next(struct rhashtable_iter *iter) > > > bool rhlist = ht->rhlist; > > > > > > if (p) { > > > - if (!rhlist || !(list = rcu_dereference(list->next))) { > > > - p = rcu_dereference(p->next); > > > - list = container_of(p, struct rhlist_head, rhead); > > > - } > > > - if (!rht_is_a_nulls(p)) { > > > - iter->skip++; > > > - iter->p = p; > > > - iter->list = list; > > > - return rht_obj(ht, rhlist ? &list->rhead : p); > > > + if (!rhlist && iter->p_is_unsafe) { > > > + /* > > > + * First time next() was called after start(). > > > + * Need to find location of 'p' in the list. > > > + */ > > > + struct rhash_head *p; > > > + > > > + iter->skip = 0; > > > + rht_for_each_rcu(p, iter->walker.tbl, iter->slot) { > > > + iter->skip++; > > > + if (p <= iter->p) > > > + continue; > > > > Out of sheer ignorance, I really don't understand the goal of the above > > conditional ?!? > > I hoped the patch description would cover that: > With this patch: > - a new object is always inserted after the last object with a > smaller address, or at the start. This preserves the property, > important when allowing objects to be removed and re-added, that > an object is never inserted *after* a position that it previously > held in the list. > > The items in each table slot are stored in order of the address of the > item. So to find the first item in a slot that was not before the > previously returned item (iter->p), we step forward while this item is > <= that one. > > Does that help at all?
Yes, it's very clear. Before I dumbly skipped some slices of the patch.
Thanks,
Paolo
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