Hi, Paul!
On 25.05.2013 15:37, Paul E. McKenney wrote:
Again, I believe that your retry logic needs to extend back into the
calling function for your some_func() example above.
And what do you think about the following approach (diff below)?
It seems to me, it's enough clear (especially with good accompanying comments)
and produces a good binary code (without significant overhead).
Also, we will remove a hidden reef in using rcu-protected (h)list traverses
with restarts.
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 6f95e24..8d8b1eb 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -269,7 +269,8 @@ static inline void list_splice_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) \
- for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
+ for (ACCESS_ONCE(*(head)), \
+ pos = list_entry_rcu((head)->next, typeof(*pos), member); \
&pos->member != (head); \
pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
@@ -459,7 +460,8 @@ static inline void hlist_add_after_rcu(struct hlist_node
*prev,
* as long as the traversal is guarded by rcu_read_lock().
*/
#define hlist_for_each_entry_rcu(tpos, pos, head, member) \
- for (pos = rcu_dereference_raw(hlist_first_rcu(head)); \
+ for (ACCESS_ONCE(*(head)), \
+ pos = rcu_dereference_raw(hlist_first_rcu(head)); \
pos && \
({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \
pos = rcu_dereference_raw(hlist_next_rcu(pos)))
@@ -476,7 +478,7 @@ static inline void hlist_add_after_rcu(struct hlist_node
*prev,
* as long as the traversal is guarded by rcu_read_lock().
*/
#define hlist_for_each_entry_rcu_bh(tpos, pos, head, member) \
- for (pos = rcu_dereference_bh((head)->first); \
+ for (ACCESS_ONCE(*(head)), pos = rcu_dereference_bh((head)->first); \
pos && \
({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \
pos = rcu_dereference_bh(pos->next))
diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
index 2ae1371..4af5ee5 100644
--- a/include/linux/rculist_nulls.h
+++ b/include/linux/rculist_nulls.h
@@ -107,7 +107,8 @@ static inline void hlist_nulls_add_head_rcu(struct
hlist_nulls_node *n,
*
*/
#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member)
\
- for (pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));
\
+ for (ACCESS_ONCE(*(head)),
\
+ pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));
\
(!is_a_nulls(pos)) &&
\
({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; });
\
pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
---
Thanks!
Regards,
Roman
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