Messages in this thread Patch in this message | | | Date | Mon, 27 May 2013 21:55:29 +0400 | From | Roman Gushchin <> | Subject | Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro |
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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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