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SubjectRe: Fix 80d20d35af1e ("nohz: Fix local_timer_softirq_pending()") may have revealed another problem
On Wed, Jan 09, 2019 at 11:20:50PM +0100, Heiner Kallweit wrote:
> 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?

Yep, I'll cook up a proper changelog and let Thomas judge if the change is worth.

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