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    SubjectRe: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset()
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    On Wed, Jan 6, 2016 at 9:34 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
    > On Wed, 6 Jan 2016, John Stultz 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.
    >>
    >> 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.
    >
    > We could also extend the fast timekeeper with boot/real/tai extensions and use
    > that for printk. You can use ktime_get_mono_fast_ns() today.

    Ack. There'd be a chance for odd values around when the time is set,
    but for debug printks I think its not critical.

    thanks
    -john


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