Messages in this thread | | | Date | Wed, 6 Jan 2016 09:33:27 -0800 | Subject | Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() | From | John Stultz <> |
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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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