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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/
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    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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      Last update: 2005-10-15 05:28    [W:0.028 / U:179.968 seconds]
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