Messages in this thread Patch in this message | | | Date | Sun, 3 Dec 2006 00:25:17 +0300 | From | Oleg Nesterov <> | Subject | PATCH? rcu_do_batch: fix a pure theoretical memory ordering race |
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On top of rcu-add-a-prefetch-in-rcu_do_batch.patch
rcu_do_batch:
struct rcu_head *next, *list;
while (list) { next = list->next; <------ [1] list->func(list); list = next; }
We can't trust *list after list->func() call, that is why we load list->next beforehand. However I suspect in theory this is not enough, suppose that
- [1] is stalled
- list->func() marks *list as unused in some way
- another CPU re-uses this rcu_head and dirties it
- [1] completes and gets a wrong result
This means we need a barrier in between. mb() looks more suitable, but I think rmb() should suffice.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- 19-rc6/kernel/rcupdate.c~rdp 2006-12-02 20:46:03.000000000 +0300 +++ 19-rc6/kernel/rcupdate.c 2006-12-02 21:04:12.000000000 +0300 @@ -236,6 +236,8 @@ static void rcu_do_batch(struct rcu_data list = rdp->donelist; while (list) { next = list->next; + /* complete the load above before we call ->func() */ + smp_rmb(); prefetch(next); list->func(list); list = next; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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