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SubjectRe: [RFC 1/6] rcu: Add support for consolidated-RCU reader checking
On Mon, Jun 03, 2019 at 10:18:47AM -0400, Joel Fernandes 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.

Actually was able to roll the if/else into its own macro as well, thus
keeping it clean. thanks!

---8<-----------------------

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index b641fdd9f1a2..cc9c382b080c 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -43,7 +43,11 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
/*
* Check during list traversal that we are within an RCU reader
*/
-#define __list_check_rcu() \
+
+#define SIXTH_ARG(a1, a2, a3, a4, a5, a6, ...) a6
+#define COUNT_VARGS(...) SIXTH_ARG(dummy, ## __VA_ARGS__, 4, 3, 2, 1, 0)
+
+#define __list_check_rcu_nocond() \
RCU_LOCKDEP_WARN(!rcu_read_lock_any_held(), \
"RCU-list traversed in non-reader section!")

@@ -59,6 +63,16 @@ static inline void __list_check_rcu_cond(int dummy, ...)
RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),
"RCU-list traversed in non-reader section!");
}
+
+#define __list_check_rcu(cond...) \
+ ({ \
+ if (COUNT_VARGS(cond) != 0) { \
+ __list_check_rcu_cond(0, ## cond); \
+ } else { \
+ __list_check_rcu_nocond(); \
+ } \
+ })
+
/*
* Insert a new entry between two known consecutive entries.
*
@@ -357,9 +371,6 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
member) : NULL; \
})

-#define SIXTH_ARG(a1, a2, a3, a4, a5, a6, ...) a6
-#define COUNT_VARGS(...) SIXTH_ARG(dummy, ## __VA_ARGS__, 4, 3, 2, 1, 0)
-
/**
* list_for_each_entry_rcu - iterate over rcu list of given type
* @pos: the type * to use as a loop cursor.
@@ -371,12 +382,8 @@ 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 (__list_check_rcu(cond), \
+ pos = list_entry_rcu((head)->next, typeof(*pos), member); \
&pos->member != (head); \
pos = list_entry_rcu(pos->member.next, typeof(*pos), member))

@@ -649,12 +656,8 @@ 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 (__list_check_rcu(cond), \
+ 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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