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SubjectRe: [RFC 1/6] rcu: Add support for consolidated-RCU reader checking
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(); \
+ } \
+ }), \
+ pos = list_entry_rcu((head)->next, typeof(*pos), member); \
&pos->member != (head); \
pos = list_entry_rcu(pos->member.next, typeof(*pos), member))

@@ -649,12 +653,15 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
* 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)),\
+ for ( \
+ ({ \
+ if (COUNT_VARGS(cond) != 0) { \
+ __list_check_rcu_cond(0, ## cond); \
+ } else { \
+ __list_check_rcu_nocond(); \
+ } \
+ }), \
+ pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
typeof(*(pos)), member); \
pos; \
pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
--
2.22.0.rc1.311.g5d7573a151-goog
\
 
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