On Sat, Oct 15, 2005 at 01:22:41PM +1000, Herbert Xu wrote:
> Hi Paul:
>
> On Sat, Oct 15, 2005 at 12:39:18PM +1000, herbert wrote:
> >
> > Besides, the expression
> >
> > i = foo(i)
> >
> > where foo has side-effects is pretty normal.
>
> Actually I've changed my mind on this. I think your version is
> better because the side-effect of rcu_dereference will cause the
> above assignment to occur twice when i refers to a memory-backed
> variable.
>
> Since all current prefetch implementations are safe as far as
> side-effects are concerned, here is an updated version that
> doesn't do i = foo(i).
>
> Andrew, please replace the previous version with this.
Looks great to me!
Thanx, Paul
Acked-by: <[email protected]>
> Thanks,
> --
> Visit Openswan at http://www.openswan.org/
> Email: Herbert Xu ~{PmV>HI~} <[email protected]>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
> diff --git a/include/linux/list.h b/include/linux/list.h
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -442,12 +442,14 @@ static inline void list_splice_init(stru
> * as long as the traversal is guarded by rcu_read_lock().
> */
> #define list_for_each_rcu(pos, head) \
> - for (pos = (head)->next; prefetch(pos->next), pos != (head); \
> - pos = rcu_dereference(pos->next))
> + for (pos = (head)->next; \
> + prefetch(rcu_dereference(pos)->next), pos != (head); \
> + pos = pos->next)
>
> #define __list_for_each_rcu(pos, head) \
> - for (pos = (head)->next; pos != (head); \
> - pos = rcu_dereference(pos->next))
> + for (pos = (head)->next; \
> + rcu_dereference(pos) != (head); \
> + pos = pos->next)
>
> /**
> * list_for_each_safe_rcu - iterate over an rcu-protected list safe
> @@ -461,8 +463,9 @@ static inline void list_splice_init(stru
> * as long as the traversal is guarded by rcu_read_lock().
> */
> #define list_for_each_safe_rcu(pos, n, head) \
> - for (pos = (head)->next, n = pos->next; pos != (head); \
> - pos = rcu_dereference(n), n = pos->next)
> + for (pos = (head)->next; \
> + n = rcu_dereference(pos)->next, pos != (head); \
> + pos = n)
>
> /**
> * list_for_each_entry_rcu - iterate over rcu list of given type
> @@ -474,11 +477,11 @@ static inline void list_splice_init(stru
> * the _rcu list-mutation primitives such as list_add_rcu()
> * as long as the traversal is guarded by rcu_read_lock().
> */
> -#define list_for_each_entry_rcu(pos, head, member) \
> - for (pos = list_entry((head)->next, typeof(*pos), member); \
> - prefetch(pos->member.next), &pos->member != (head); \
> - pos = rcu_dereference(list_entry(pos->member.next, \
> - typeof(*pos), member)))
> +#define list_for_each_entry_rcu(pos, head, member) \
> + for (pos = list_entry((head)->next, typeof(*pos), member); \
> + prefetch(rcu_dereference(pos)->member.next), \
> + &pos->member != (head); \
> + pos = list_entry(pos->member.next, typeof(*pos), member))
>
>
> /**
> @@ -492,8 +495,9 @@ static inline void list_splice_init(stru
> * as long as the traversal is guarded by rcu_read_lock().
> */
> #define list_for_each_continue_rcu(pos, head) \
> - for ((pos) = (pos)->next; prefetch((pos)->next), (pos) != (head); \
> - (pos) = rcu_dereference((pos)->next))
> + for ((pos) = (pos)->next; \
> + prefetch(rcu_dereference((pos))->next), (pos) != (head); \
> + (pos) = (pos)->next)
>
> /*
> * Double linked lists with a single pointer list head.
> @@ -696,8 +700,9 @@ static inline void hlist_add_after_rcu(s
> pos = n)
>
> #define hlist_for_each_rcu(pos, head) \
> - for ((pos) = (head)->first; pos && ({ prefetch((pos)->next); 1; }); \
> - (pos) = rcu_dereference((pos)->next))
> + for ((pos) = (head)->first; \
> + rcu_dereference((pos)) && ({ prefetch((pos)->next); 1; }); \
> + (pos) = (pos)->next)
>
> /**
> * hlist_for_each_entry - iterate over list of given type
> @@ -762,9 +767,9 @@ static inline void hlist_add_after_rcu(s
> */
> #define hlist_for_each_entry_rcu(tpos, pos, head, member) \
> for (pos = (head)->first; \
> - pos && ({ prefetch(pos->next); 1;}) && \
> + rcu_dereference(pos) && ({ prefetch(pos->next); 1;}) && \
> ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
> - pos = rcu_dereference(pos->next))
> + pos = pos->next)
>
> #else
> #warning "don't include kernel headers in userspace"
-
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