On Fri, 15 Feb 2019 11:22:45 +0000
Vlad Buslov <vla...@mellanox.com> wrote:
> On Thu 14 Feb 2019 at 20:34, Stefano Brivio <sbri...@redhat.com> wrote:
> > On Thu, 14 Feb 2019 09:47:03 +0200
> > Vlad Buslov <vla...@mellanox.com> wrote:
> >
> >> +static struct cls_fl_filter *fl_get_next_filter(struct tcf_proto *tp,
> >> + unsigned long *handle)
> >> +{
> >> + struct cls_fl_head *head = fl_head_dereference(tp);
> >> + struct cls_fl_filter *f;
> >> +
> >> + rcu_read_lock();
> >> + /* don't return filters that are being deleted */
> >> + while ((f = idr_get_next_ul(&head->handle_idr,
> >> + handle)) != NULL &&
> >> + !refcount_inc_not_zero(&f->refcnt))
> >> + ++(*handle);
> >
> > This... hurts :) What about:
> >
> > while ((f = idr_get_next_ul(&head->handle_idr, &handle))) {
> > if (refcount_inc_not_zero(&f->refcnt))
> > break;
> > ++(*handle);
> > }
> >
> > ?
>
> I prefer to avoid using value of assignment as boolean and
> non-structured jumps, when possible. In this case it seems OK either
> way, but how about:
>
> for (f = idr_get_next_ul(&head->handle_idr, handle);
> f && !refcount_inc_not_zero(&f->refcnt);
> f = idr_get_next_ul(&head->handle_idr, handle))
> ++(*handle);
Honestly, I preferred the original, this is repeating idr_get_next_ul()
twice.
Maybe, just:
[...]
struct idr *idr;
[...]
idr = &head->handle_idr;
while ((f = idr_get_next_ul(idr, handle)) != NULL &&
!refcount_inc_not_zero(&f->refcnt))
++(*handle);
also rather ugly, but not entirely unreadable. I tried drafting a
helper for this, but it just ends up hiding what this does.
> >> @@ -1349,6 +1404,7 @@ static int fl_change(struct net *net, struct sk_buff
> >> *in_skb,
> >> err = -ENOBUFS;
> >> goto errout_tb;
> >> }
> >> + refcount_set(&fnew->refcnt, 1);
> >>
> >> err = tcf_exts_init(&fnew->exts, TCA_FLOWER_ACT, 0);
> >> if (err < 0)
> >> @@ -1381,6 +1437,7 @@ static int fl_change(struct net *net, struct sk_buff
> >> *in_skb,
> >> if (!tc_in_hw(fnew->flags))
> >> fnew->flags |= TCA_CLS_FLAGS_NOT_IN_HW;
> >>
> >> + refcount_inc(&fnew->refcnt);
> >
> > I guess I'm not getting the semantics but... why is it 2 now?
>
> As soon as fnew is inserted into head->handle_idr (one reference), it
> becomes accessible to concurrent users, which means that it can be
> deleted at any time. However, tp->change() returns a reference to newly
> created filter to cls_api by assigning "arg" parameter to it (second
> reference). After tp->change() returns, cls API continues to use fnew
> and releases it with tfilter_put() when finished.
I see, thanks for the explanation!
--
Stefano
