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SubjectRe: Fix 80d20d35af1e ("nohz: Fix local_timer_softirq_pending()") may have revealed another problem
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On 28.12.2018 07:39, Heiner Kallweit wrote:
> On 28.12.2018 07:34, Heiner Kallweit wrote:
>> On 28.12.2018 02:31, Frederic Weisbecker wrote:
>>> On Fri, Dec 28, 2018 at 12:11:12AM +0100, Heiner Kallweit wrote:
>>>>
>> [...]
>>>
>>> Interesting, the softirq is raised from hardirq but it's not handled in the end of
>>> the IRQ. Are you running threaded IRQS by any chance? If so I would expect ksoftirqd
>>> to handle the pending work before we go idle. However I can imagine a small window
>>> where such an expectation may not be met: if the softirq is raised after the ksoftirqd
>>> thread is parked (CPUHP_AP_SMPBOOT_THREADS), which is right before we disable the CPU
>>> (CPUHP_TEARDOWN_CPU).
>>>
>> I have a network driver (r8169) using NAPI which runs in softirq context AFAIK.
>> For testing purposes I sometimes trigger system suspend via network, so there is
>> network adapter activity when system suspends. Apart from that nothing really
>> exciting:
>> CPU0 CPU1 CPU2 CPU3
>> 0: 43 0 0 0 IO-APIC 2-edge timer
>> 1: 4 0 0 0 IO-APIC 1-edge i8042
>> 8: 0 1 0 0 IO-APIC 8-fasteoi rtc0
>> 9: 0 0 0 0 IO-APIC 9-fasteoi acpi
>> 12: 0 0 0 5 IO-APIC 12-edge i8042
>> 120: 0 0 0 0 PCI-MSI 311296-edge PCIe PME
>> 121: 0 0 0 0 PCI-MSI 315392-edge PCIe PME
>> 122: 0 0 0 0 PCI-MSI 327680-edge PCIe PME
>> 123: 0 0 3328 0 PCI-MSI 294912-edge ahci[0000:00:12.0]
>> 124: 0 133 0 0 PCI-MSI 344064-edge xhci_hcd
>> 125: 0 0 32 0 PCI-MSI 245760-edge mei_me
>> 127: 381 0 0 0 PCI-MSI 1572864-edge enp3s0
>> 128: 0 0 0 236 PCI-MSI 32768-edge i915
>> 129: 0 374 0 0 PCI-MSI 229376-edge snd_hda_intel:card0
>>
>>> I don't know if we can afford to ignore a softirq even at this late stage. We should
>>> probably avoid leaking any. So here is a possible fix, if you don't mind trying:
>>>
>> I tested your patch and at least in the first minutes of testing couldn't reproduce
>> the issue any longer. I tested manual system suspend and the following script you
>> sent when we started to analyze the issue.
>>
>
> Also after some more time the issue didn't occur again. So it seems your analysis
> was right and also the approach to fix it. Thanks!
> Will let you know in case the issue should pop up again under special
> circumstances.
>
Frederic, so far this fix didn't appear in linux-next, are you going to submit it?

>
>> Heiner
>>
>> --------------------------------------------------------------------------
>>
>> #!/bin/bash
>>
>> do_hotplug()
>> {
>> for i in $(seq 1 $2)
>> do
>> echo $1 > /sys/devices/system/cpu/cpu$i/online
>> done
>> }
>>
>> LAST_CPU=$(($(nproc)-1))
>>
>> while true
>> do
>> do_hotplug 0 $LAST_CPU
>> do_hotplug 1 $LAST_CPU
>> done
>>
>

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