On Fri, 24 Aug 2018, Greg KH wrote:
> On Thu, Aug 23, 2018 at 05:57:06PM -0500, Grygorii Strashko wrote:
> > This patch was back ported to the Stable linux-4.14.y and It causes regression -
> > flood of "NOHZ: local_softirq_pending" messages on all TI boards during boot (NFS boot):
> >
> > [ 4.179796] NOHZ: local_softirq_pending 2c2 in sirq 256
> > [ 4.185051] NOHZ: local_softirq_pending 2c2 in sirq 256
This printout is weird. Did you add something here?
> > the same is not reproducible with LKML - seems due to changes in tick-sched.c
> > __tick_nohz_idle_enter()/tick_nohz_irq_exit().
>
> What changes do you think fixed this?
>
> > I've generated backtrace from can_stop_idle_tick() (see below) and seems this
> > patch makes tick_nohz_irq_exit() call unconditional in case of nested interrupt:
> >
> > gic_handle_irq
> > |- irq_exit
> > |- preempt_count_sub(HARDIRQ_OFFSET); <-- [1]
> > |-__do_softirq
> > <irqs enabled>
> > |- gic_handle_irq()
> > |- irq_exit()
> > |- tick_irq_exit()
> > if (!in_irq()) <-- My understanding is that this condition will be always true due to [1]
Correct, but that's not the problem. The issue is that this happens in a
softirq disabled region. Does the below fix it?
Thanks,
tglx
8<--------------------
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 5b33e2f5c0ed..6aab9d54a331 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -888,7 +888,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
static int ratelimit;
- if (ratelimit < 10 &&
+ if (ratelimit < 10 && !in_softirq() &&
(local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
pr_warn("NOHZ: local_softirq_pending %02x\n",
(unsigned int) local_softirq_pending());
