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Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset()

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On Wed, Jan 6, 2016 at 9:28 AM, John Stultz <john.stultz@linaro.org> wrote:
> On Wed, Jan 6, 2016 at 5:00 AM, Prarit Bhargava <prarit@redhat.com> wrote:
>> -ktime_t ktime_get_with_offset(enum tk_offsets offs)
>> +ktime_t ktime_get_with_offset(enum tk_offsets offs, int trylock)
>>  {
>>         struct timekeeper *tk = &tk_core.timekeeper;
>>         unsigned int seq;
>>         ktime_t base, *offset = offsets[offs];
>>         s64 nsecs;
>> +       unsigned long flags = 0;
>> +
>> +       if (unlikely(!timekeeping_initialized))
>> +               return ktime_set(0, 0);
>>
>>         WARN_ON(timekeeping_suspended);
>>
>> +       if (trylock && !raw_spin_trylock_irqsave(&timekeeper_lock, flags))
>> +               return ktime_set(KTIME_MAX, 0);
>
> Wait.. this doesn't make sense. The timekeeper lock is only for reading.

Only for writing.. sorry.. still drinking my coffee.

> What I was suggesting to you off line is to have something that avoids
> spinning on the seqcounter should if a bug occurs and we IPI all the
> cpus, that we don't deadlock or block any printk messages.

And more clearly here, if a cpu takes a write on the seqcounter in
update_wall_time() and at that point another cpu hits a bug, and IPIs
the cpus, the system would deadlock. That's really what I want to
avoid.

thanks
-john
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[PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() Prarit Bhargava <prarit@redhat.com> - 2016-01-06 14:10 +0100
  Re: [PATCH 1/2] kernel, timekeeping, add trylock option to  ktime_get_with_offset() Jiri Bohac <jbohac@suse.cz> - 2016-01-06 17:10 +0100
    Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() Prarit Bhargava <prarit@redhat.com> - 2016-01-06 17:30 +0100
  Re: [PATCH 1/2] kernel, timekeeping, add trylock option to  ktime_get_with_offset() Petr Mladek <pmladek@suse.com> - 2016-01-06 17:30 +0100
  Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() John Stultz <john.stultz@linaro.org> - 2016-01-06 18:30 +0100
    Re: [PATCH 1/2] kernel, timekeeping, add trylock option to  ktime_get_with_offset() Thomas Gleixner <tglx@linutronix.de> - 2016-01-06 18:40 +0100
      Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() Prarit Bhargava <prarit@redhat.com> - 2016-01-06 19:10 +0100
        Re: [PATCH 1/2] kernel, timekeeping, add trylock option to  ktime_get_with_offset() Thomas Gleixner <tglx@linutronix.de> - 2016-01-06 19:20 +0100
      Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() John Stultz <john.stultz@linaro.org> - 2016-01-06 20:10 +0100
        Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() Prarit Bhargava <prarit@redhat.com> - 2016-01-06 20:10 +0100
    Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() John Stultz <john.stultz@linaro.org> - 2016-01-06 18:40 +0100
      Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() Prarit Bhargava <prarit@redhat.com> - 2016-01-06 19:10 +0100
        Re: [PATCH 1/2] kernel, timekeeping, add trylock option to  ktime_get_with_offset() Thomas Gleixner <tglx@linutronix.de> - 2016-01-06 19:20 +0100

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