On Tue, Jun 04, 2019 at 06:53:58AM -0400, Steven Rostedt wrote:
> On Mon, 3 Jun 2019 10:18:47 -0400
> Joel Fernandes <j...@joelfernandes.org> wrote:
>
> > On Mon, Jun 03, 2019 at 10:01:28AM +0200, Peter Zijlstra wrote:
> > > On Sat, Jun 01, 2019 at 06:27:33PM -0400, Joel Fernandes (Google) wrote:
> > > > +#define list_for_each_entry_rcu(pos, head, member, cond...)
> > > > \
> > > > + if (COUNT_VARGS(cond) != 0) {
> > > > \
> > > > + __list_check_rcu_cond(0, ## cond);
> > > > \
> > > > + } else {
> > > > \
> > > > + __list_check_rcu();
> > > > \
> > > > + }
> > > > \
> > > > + for (pos = list_entry_rcu((head)->next, typeof(*pos), member);
> > > > \
> > > > + &pos->member != (head);
> > > > \
> > > > pos = list_entry_rcu(pos->member.next, typeof(*pos),
> > > > member))
> > > >
> > > > /**
> > > > @@ -621,7 +648,12 @@ static inline void hlist_add_behind_rcu(struct
> > > > hlist_node *n,
> > > > * the _rcu list-mutation primitives such as hlist_add_head_rcu()
> > > > * as long as the traversal is guarded by rcu_read_lock().
> > > > */
> > > > +#define hlist_for_each_entry_rcu(pos, head, member, cond...)
> > > > \
> > > > + if (COUNT_VARGS(cond) != 0) {
> > > > \
> > > > + __list_check_rcu_cond(0, ## cond);
> > > > \
> > > > + } else {
> > > > \
> > > > + __list_check_rcu();
> > > > \
> > > > + }
> > > > \
> > > > for (pos = hlist_entry_safe
> > > > (rcu_dereference_raw(hlist_first_rcu(head)),\
> > > > typeof(*(pos)), member);
> > > > \
> > > > pos;
> > > > \
> > >
> > >
> > > This breaks code like:
> > >
> > > if (...)
> > > list_for_each_entry_rcu(...);
> > >
> > > as they are no longer a single statement. You'll have to frob it into
> > > the initializer part of the for statement.
> >
> > Thanks a lot for that. I fixed it as below (diff is on top of the patch):
> >
> > If not for that '##' , I could have abstracted the whole if/else
> > expression into its own macro and called it from list_for_each_entry_rcu()
> > to
> > keep it more clean.
> >
> > ---8<-----------------------
> >
> > diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> > index b641fdd9f1a2..cc742d294bb0 100644
> > --- a/include/linux/rculist.h
> > +++ b/include/linux/rculist.h
> > @@ -371,12 +372,15 @@ static inline void list_splice_tail_init_rcu(struct
> > list_head *list,
> > * as long as the traversal is guarded by rcu_read_lock().
> > */
> > #define list_for_each_entry_rcu(pos, head, member, cond...)
> > \
> > - if (COUNT_VARGS(cond) != 0) { \
> > - __list_check_rcu_cond(0, ## cond); \
> > - } else { \
> > - __list_check_rcu(); \
> > - } \
> > - for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
> > + for ( \
> > + ({ \
> > + if (COUNT_VARGS(cond) != 0) { \
> > + __list_check_rcu_cond(0, ## cond); \
> > + } else { \
> > + __list_check_rcu_nocond(); \
> > + } \
> > + }), \
>
> For easier to read I would do something like this:
>
> #define check_rcu_list(cond) \
> ({ \
> if (COUNT_VARGS(cond) != 0) \
> __list_check_rcu_cond(0, ## cond); \
> else \
> __list_check_rcu_nocond(); \
> })
>
> #define list_for_each_entry_rcu(pos, head, member, cond...) \
> for (check_rcu_list(cond), \
Yes, already doing it this way as I replied to Peter here:
https://lore.kernel.org/patchwork/patch/1082846/#1278489
Thanks!
- Joel
