Messages in this thread | | | Date | Mon, 4 Dec 2006 01:12:27 +0300 | From | Oleg Nesterov <> | Subject | Re: PATCH? rcu_do_batch: fix a pure theoretical memory ordering race |
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On 12/03, Eric Dumazet wrote: > > Oleg Nesterov a ?crit : > > Yes, but how is it related to RCU ? > I mean, rcu_do_batch() is just a loop like others in kernel. > The loop itself is not buggy, but can call a buggy function, you are right.
int start_me_again;
struct rcu_head rcu_head;
void rcu_func(struct rcu_head *rcu) { start_me_again = 1; }
// could be called on arbitrary CPU void check_start_me_again(void) { static spinlock_t lock;
spin_lock(lock); if (start_me_again) { start_me_again = 0; call_rcu(&rcu_head, rcu_func); } spin_unlock(lock); }
I'd say this code is not buggy.
In case it was not clear. I do not claim we need this patch (I don't know). And yes, I very much doubt we can hit this problem in practice (even if I am right).
What I don't agree with is that it is callback which should take care of this problem.
> A smp_rmb() wont avoid all possible bugs...
For example?
Oleg.
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