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author | Herbert Xu <herbert@gondor.apana.org.au> | 2005-10-17 05:29:20 +0200 |
---|---|---|
committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-10-17 17:59:10 +0200 |
commit | b24d18aa743dad0c42918157c5d717686269d3a8 (patch) | |
tree | ceade1641a1806c5f3db2f4b344fe9070b488bad | |
parent | Fix memory ordering bug in page reclaim (diff) | |
download | linux-b24d18aa743dad0c42918157c5d717686269d3a8.tar.xz linux-b24d18aa743dad0c42918157c5d717686269d3a8.zip |
[PATCH] list: add missing rcu_dereference on first element
It seems that all the list_*_rcu primitives are missing a memory barrier
on the very first dereference. For example,
#define list_for_each_rcu(pos, head) \
for (pos = (head)->next; prefetch(pos->next), pos != (head); \
pos = rcu_dereference(pos->next))
It will go something like:
pos = (head)->next
prefetch(pos->next)
pos != (head)
do stuff
We're missing a barrier here.
pos = rcu_dereference(pos->next)
fetch pos->next
barrier given by rcu_dereference(pos->next)
store pos
Without the missing barrier, the pos->next value may turn out to be stale.
In fact, if "do stuff" were also dereferencing pos and relying on
list_for_each_rcu to provide the barrier then it may also break.
So here is a patch to make sure that we have a barrier for the first
element in the list.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r-- | include/linux/list.h | 39 |
1 files changed, 22 insertions, 17 deletions
diff --git a/include/linux/list.h b/include/linux/list.h index e6ec59682274..084971f333fe 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -442,12 +442,14 @@ static inline void list_splice_init(struct list_head *list, * 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(struct list_head *list, * 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(struct list_head *list, * 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(struct list_head *list, * 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(struct hlist_node *prev, 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(struct hlist_node *prev, */ #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" |