2012/11/28 Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>: > Thank you all for the review and education. > > Below are my current understandings and an update version. Would you > please help to review it again and give your comments? > > Thanks, Zhong > > Now it seems to me that it is legal to call rcu_irq_exit/enter() without > a matching rcu_irq_enter/exit() if the cpu is in non rcu idle state. > > As opposite, it is illegal to call rcu_irq_exit() without a matching > rcu_irq_enter() if the cpu is in rcu idle state. > > But it seems legal to call rcu_irq_enter() without a matching > rcu_irq_exit() if the cpu is in rcu idle state, regarding the > dynticks_nesting value. However, it seems not good to exit the rcu > idle state, if we are actually entering into idle mode, so maybe it's > better to call a matching rcu_irq_exit() before actually idle? > > As Frederic pointed out, we need a rcu_user_exit() to exit the user eqs > (if we are in this state) in the beginning. But after some more > thinking, I guess we might also need to call rcu_user_enter() after the > waiting, if we get this page fault from user space. So maybe it's better > to use rcu user eqs exception hooks here? Makes sense. > > With rcu_user_exit() at the beginning, now rcu_irq_enter() only protects > the cpu idle eqs, but it's not good to call rcu_irq_exit() after the cpu > halt and the page ready. Hmm, why is it not good? > > So I still want to remove it. And later if it shows that we really needs > rcu somewhere in this code path, maybe we could use RCU_NONIDLE() to > protect it. ( The suspicious RCU usage reported in commit > c5e015d4949aa665 seems related to schedule(), which is not in the code > path if we are in cpu idle eqs ) Yes but if rcu_irq_*() calls are fine to be called there, and I believe they are because exception_enter() exits the user mode, we should start to protect there right now instead of waiting for a potential future warning of illegal RCU use. > > I think we still need Gleb's patch about the idle check in > kvm_async_pf_task_wait(), and maybe another patch for the > exit_idle()/enter_idle() issue. Right. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
