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Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job"

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Hi Eric,

On Wed, Nov 16, 2016 at 07:52:42AM -0800, Eric Dumazet wrote:
>On Wed, Nov 16, 2016 at 5:55 AM, Brian Starkey <brian.starkey@arm.com> wrote:
>> Hi,
>>
>> I'm running an ARM FVP (virtual platform - simluated hardware), which
>> is failing to reach a login prompt due to extremely slow progress
>> during boot. systemd gives up waiting for the ttyAMA0 device to
>> appear, and never starts the getty.
>>
>> I've bisected this to commit 4cd13c21b207 "softirq: Let ksoftirqd do
>> its job".
>>
>> Without this commit, the system boots to a login prompt in 2 minutes.
>> With this commit, the system eventually manages to bring up sshd after
>> 22 minutes, but as mentioned, the dev-ttyAMA0.device unit has timed
>> out and so I don't get a prompt on my console.
>>
>> I only hit the issue when my rootfs is mounted over NFS, and with only
>> a single core enabled. The (simulated) network device is an SMC91C111.
>> With multiple cores enabled or a non-NFS filesystem, everything seems
>> to work OK.
>>
>> I don't have an identical real hardware platform to try, but I
>> could not reproduce it on a real ARM Juno board, which is similar.
>>
>> It looks from the logs that udev's workers are unable to make
>> progress, so the device nodes don't get created. Don't pay too much
>> attention to the timestamps in the logs below, they are "inside" the
>> virtual platform, and don't reflect wall-clock time.
>> Log before 4cd13c21b207:
>>         https://drive.google.com/open?id=0B8siaK6ZjvEwMktoa0NUS2hJd1U
>> Log after 4cd13c21b207:
>>         https://drive.google.com/open?id=0B8siaK6ZjvEwZXlfeFFSQl9xZTQ
>> Kernel config: arch/arm64/configs/defconfig
>>
>> I'm not sure how to debug this further, so if you have any suggestions
>> I'd be glad to hear them.
>>
>> Many thanks,
>> Brian
>>
>
>Hi Brian.
>
>Thanks a lot for this report.
>
>If issue triggers when/if using one core, it is possible one driver
>has a dependency on
>softirqs being serviced during an initialization loop.
>
>If the thread is not yielding cpu (holding something like a spinlock
>thus disabling preemption),
>then ksoftirqd might not be able to run on the (same) cpu.
>

The smc91x driver does seem to have some trickiness around softirqs.
I'm not familiar with net drivers, but I'll see if I can figure
anything out there.

>I sent a patch for busy polling yesterday, but I am almost certain
>this would not fix your issue
>(assuming you have CONFIG_PREEMPT)
>
>https://patchwork.ozlabs.org/patch/695185/

You're right in saying that this didn't help.

Thanks,
Brian

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Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Brian Starkey <brian.starkey@arm.com> - 2016-11-16 15:00 +0100
  Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Eric Dumazet <edumazet@google.com> - 2016-11-16 17:00 +0100
    Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Brian Starkey <brian.starkey@arm.com> - 2016-11-16 19:10 +0100
      Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Eric Dumazet <edumazet@google.com> - 2016-11-16 19:50 +0100
        Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Brian Starkey <brian.starkey@arm.com> - 2016-11-16 22:10 +0100
          Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Brian Starkey <brian.starkey@arm.com> - 2016-11-17 18:10 +0100
            Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Thomas Gleixner <tglx@linutronix.de> - 2016-11-18 01:50 +0100
              Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Brian Starkey <brian.starkey@arm.com> - 2016-11-18 21:30 +0100
              Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Brian Starkey <brian.starkey@arm.com> - 2016-11-22 11:40 +0100
                Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Eric Dumazet <edumazet@google.com> - 2016-11-22 15:30 +0100
                Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Brian Starkey <brian.starkey@arm.com> - 2016-11-22 16:30 +0100
                Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Eric Dumazet <edumazet@google.com> - 2016-11-22 17:20 +0100
                Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Brian Starkey <brian.starkey@arm.com> - 2016-11-23 19:30 +0100
                Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Eric Dumazet <edumazet@google.com> - 2016-11-23 21:10 +0100
          Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let  ksoftirqd do its job" Eric Dumazet <edumazet@google.com> - 2016-11-17 18:10 +0100

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