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. -- Steve