On Wed, 16 Oct 2013 15:08:57 +0200 Frederic Weisbecker <fweis...@gmail.com> wrote:
> Faults can call rcu_user_exit() / rcu_user_enter(). This is not supposed to > happen > between rcu_nmi_enter() and rcu_nmi_exit(). rdtp->dynticks would be > incremented in the > wrong way. > > Ah but we have an in_interrupt() check in context_tracking_user_enter() that > protects > us against that. I will say that we should probably warn if it's any fault other than a vmalloc fault. A vmalloc fault should only happen in kernel space, and should not be happening from user code. > > > > > > > > > So I hope we can think about something else for the long term. > > > > I still don't understand what's wrong with it. As long as the faulting > > code does not grab any locks there shouldn't be anything wrong with > > faulting in NMI. For vmalloc, it is just updating page tables. > > NMI code is written with the idea that it can't be interrupted. May be that > paranoia (again), you know. And I can't point you any problem in practice. > I just think that allowing such a thing is asking for troubles. The WARN_ON() that I removed is from vmalloc fault. I don't see an issue with NMIs faulting via vmalloc. For any other page fault, sure, I would be concerned about it. But what's wrong with an NMI running module code? > > But I'm ok with your patch, it fixes a real bug and as long as we don't have > a better solution, we should keep that. > > BTW, does faulting in NMIs re-enable NMIs? Yes, but we now have code to handle that :-) -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
