On Sat, Aug 25, 2012 at 06:56:29PM +0200, Daniel Wagner wrote: > On 25.08.2012 01:26, Tejun Heo wrote: > >On Fri, Aug 24, 2012 at 04:01:37PM +0200, Daniel Wagner wrote: > >>@@ -306,6 +312,11 @@ static void __exit exit_cgroup_cls(void) > >> synchronize_rcu(); > >> #endif > >> > >>+#if IS_MODULE(CONFIG_NET_CLS_CGROUP) > >>+ static_key_slow_dec(&cgroup_cls_enabled); > >>+ rcu_barrier(); > > > >Why is this rcu_barrier() necessary? > > I have read the rcubarrier.txt document and I got from that that an > rcu_barrier() is needed when unloading a module. But maybe I got it > wrong. > > So the idea after disabling the jump lables all pending readers in > task_cls_classid() have left. THe same thing is done in the old code > with the dynamic id part. With the difference that synchronize_rcu() > is used. FWIW, the rcu_barrier() is needed only if the module uses call_rcu(). In that case it is required to ensure that all the resulting callbacks execute before the module's .text is freed up. Thanx, Paul > >In general, please explain what > >synchronization is going on when using sync constructs which aren't > >obvious - e.g. memory barriers, rcu barriers. > > Sure, I will keep this in mind. > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
