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

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Date:   Sun, 19 Aug 2018 00:34:09 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: Fix 80d20d35af1e ("nohz: Fix local_timer_softirq_pending()") may
 have revealed another problem

On 18.08.2018 13:26, Thomas Gleixner wrote:
> On Thu, 16 Aug 2018, 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.
> 
> Looks so. That seems to be related to CPU offlining. No idea yet...
> 
I checked a little further and at the time the warning is printed the
cpu is still online but not active any longer.
I can avoid the warning with the following change, but as a
disclaimer: I have no clue of this subsystem and don't know what
I'm doing ..

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 5b33e2f5c..19a030e40 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -862,13 +862,13 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts)
 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 {
 	/*
-	 * If this CPU is offline and it is the one which updates
+	 * If this CPU is inactive and it is the one which updates
 	 * jiffies, then give up the assignment and let it be taken by
 	 * the CPU which runs the tick timer next. If we don't drop
 	 * this here the jiffies might be stale and do_timer() never
 	 * invoked.
 	 */
-	if (unlikely(!cpu_online(cpu))) {
+	if (unlikely(!cpu_active(cpu))) {
 		if (cpu == tick_do_timer_cpu)
 			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
 		/*
-- 



>> 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
>>
>