On 09/24, Paul E. McKenney wrote: > > On Tue, Sep 24, 2013 at 07:06:31PM +0200, Oleg Nesterov wrote: > > > > If gcc can actually do something wrong, then I suspect this barrier() > > should be unconditional. > > If you are saying that there should be a barrier() on all return paths > from get_online_cpus(), I agree. Paul, Peter, could you provide any (even completely artificial) example to explain me why do we need this barrier() ? I am puzzled. And preempt_enable() already has barrier... get_online_cpus(); do_something(); Yes, we need to ensure gcc doesn't reorder this code so that do_something() comes before get_online_cpus(). But it can't? At least it should check current->cpuhp_ref != 0 first? And if it is non-zero we do not really care, we are already in the critical section and this ->cpuhp_ref has only meaning in put_online_cpus(). Confused... Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>