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SubjectRe: [LIST] Add missing rcu_dereference on first element
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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.

Thanks,
--
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txtdiff --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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