Re: Fix 80d20d35af1e ("nohz: Fix local_timer_softirq_pending()") may have revealed another problem

[Thomas Gleixner]

On Fri, 24 Aug 2018, Heiner Kallweit wrote:
> On 24.08.2018 06:12, Frederic Weisbecker wrote:
> > On Thu, Aug 16, 2018 at 08:13:03AM +0200, Heiner Kallweit wrote:
> >> Recently I started to get warning "NOHZ: local_softirq_pending 202" and
> >> I think it's related to mentioned commit (didn't bisect it yet).
> >> See log from suspending.
> >>
> >> I have no reason to think the fix is wrong, it may just have revealed
> >> another issue which existed before and was hidden by the bug.
> >>
> >> Rgds, Heiner
> >>
> >> [   75.073353] random: crng init done
> >> [   75.073402] random: 7 urandom warning(s) missed due to ratelimiting
> >> [   78.619564] PM: suspend entry (deep)
> >> [   78.619675] PM: Syncing filesystems ... done.
> >> [   78.653684] Freezing user space processes ... (elapsed 0.002 seconds) done.
> >> [   78.656094] OOM killer disabled.
> >> [   78.656113] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
> >> [   78.658177] Suspending console(s) (use no_console_suspend to debug)
> >> [   78.663066] nuvoton-cir 00:07: disabled
> >> [   78.671817] sd 0:0:0:0: [sda] Synchronizing SCSI cache
> >> [   78.672210] sd 0:0:0:0: [sda] Stopping disk
> >> [   78.786651] ACPI: Preparing to enter system sleep state S3
> >> [   78.789613] PM: Saving platform NVS memory
> >> [   78.789759] Disabling non-boot CPUs ...
> >> [   78.805154] NOHZ: local_softirq_pending 202
> >> [   78.805182] NOHZ: local_softirq_pending 202
> >> [   78.807102] smpboot: CPU 1 is now offline
> > 
> > I've tried to reproduce with suspend on disk but got unsuccessful.
> > 
> > A small question as I see someone is having a similar issue with a stable
> > release only. On which kernel did you trigger that: upstream or stable?
> > 
> > I'll continue investigating.
> > 
> > Thanks.
> > 
> Affected is recent linux-next, after the commit mentioned in the subject.
> I can work around the warning (not sure whether it's a proper fix),
> see here:
> https://lkml.org/lkml/2018/8/18/272

Can you try the one I posted in this thread:

 https://lkml.kernel.org/r/alpine.DEB.2.21.1808240851420.1668@xxxxxxxxxxxxxxxxxxxxxxx

Also below for reference.

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());