On Thu, Mar 12, 2020 at 11:52:01PM -0400, Joel Fernandes wrote:
> On Thu, Mar 12, 2020 at 07:40:45PM -0700, paulmck@xxxxxxxxxx wrote:
> > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> >
> > The rcu_nmi_enter_common() function can be invoked both in interrupt
> > and NMI handlers. If it is invoked from process context (as opposed
> > to userspace or idle context) on a nohz_full CPU, it might acquire the
> > CPU's leaf rcu_node structure's ->lock. Because this lock is held only
> > with interrupts disabled, this is safe from an interrupt handler, but
> > doing so from an NMI handler can result in self-deadlock.
> >
> > This commit therefore adds "irq" to the "if" condition so as to only
> > acquire the ->lock from irq handlers or process context, never from
> > an NMI handler.
>
> I think Peter's new lockdep changes for NMI would also catch this issue.
>
> >
> > Fixes: 5b14557b073c ("rcu: Avoid tick_dep_set_cpu() misordering")
>
> Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Applied, thank you!!!
Thanx, Paul
> thanks,
>
> - Joel
>
>
> > Reported-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx> # 5.5.x
> > ---
> > kernel/rcu/tree.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index d3f52c3..f7d3e48 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -825,7 +825,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
> > rcu_cleanup_after_idle();
> >
> > incby = 1;
> > - } else if (tick_nohz_full_cpu(rdp->cpu) &&
> > + } else if (irq && tick_nohz_full_cpu(rdp->cpu) &&
> > rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE &&
> > READ_ONCE(rdp->rcu_urgent_qs) &&
> > !READ_ONCE(rdp->rcu_forced_tick)) {
> > --
> > 2.9.5
> >
