On Mon, Oct 02, 2017 at 03:47:48PM -0400, Steven Rostedt wrote: > On Mon, 2 Oct 2017 12:38:57 -0700 > "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > On Mon, Oct 02, 2017 at 03:33:17PM -0400, Steven Rostedt wrote: > > > > > > Paul, > > > > > > Can you backport this patch to 4.9 and 4.4 if it is required. The other > > > patches I posted (and also failed to apply, but should be backported) > > > depend on this patch, if it is an issue with those kernels. > > > > No problem! > > > > How do we determine whether or not it is required? > > Can rcu_irq_enter() be called within a rcu_nmi_enter() in these > kernels? If not, that needs to be fixed. Because nmi's can still page > fault. > > > > > Do we need to ask one of Bruce or Nick? ;-) > > > > The bug I fixed is actually there, but lockdep doesn't complain. The > module code that uses synchronize_sched() which requires RCU to be > watching when preemption is disabled. RCU isn't watching is some of > these cases that are called. Recent kernels added rcu annotations into > these preempt disabled paths which caused lockdep to report the issue. > The older kernels that had the bug just didn't have lockdep complain > about it. It turned out that one backport is needed for 4.2-4.4, and another for 4.5-4.12. I sent both. Thanx, Paul