On 27 January 2018 at 00:01, Arnd Bergmann <a...@arndb.de> wrote: > On Fri, Jan 26, 2018 at 3:20 PM, Baolin Wang <baolin.w...@linaro.org> wrote: >> On 26 January 2018 at 22:00, Daniel Thompson <daniel.thomp...@linaro.org> >> wrote: >>> On Fri, Jan 26, 2018 at 10:21:58AM +0100, Arnd Bergmann wrote: >>>> On Fri, Jan 26, 2018 at 4:03 AM, Baolin Wang <baolin.w...@linaro.org> >>>> wrote: >>>> >>>> Using ktime_get_seconds() avoids locking problems, but I wonder what >>>> would happen if we trigger the 'WARN_ON(timekeeping_suspended)' >>>> from kdb. Is that a problem? If it is, we have to use >>>> ktime_get_mono_fast_ns() >>>> and div_u64() instead. >>> >>> Normally a WARN_ON() doesn't triggered a kgdb_breakpoint() so (apart >>> from bugs) we can start executing the warning. Unfortunately >>> kdb_trap_printk isn't set when we call ktime_get_seconds() so printing >>> the warning isn't safe. >>> >>> If we had no choice of time function we could work around by >>> enabling printk() trapping for the call but since ktime_get_mono_fast_ns() >>> already exists its probably best just to use that. >>> >> >> If timekeeping_suspended is set, which means the system had been in >> suspend state. So now we still need debugger the system? But cores >> were already powered down. > > I'm not using kdb myself, but I would assume that trapping into the debugger > during a suspend/resume bug is a very important scenario. > >> The ktime_get_mono_fast_ns() will access the the clocksource driver, >> if the timekeeping is suspended following system suspend and the >> clocksource is not SUSPEND_NONSTOP, we may meet some unexpected issue >> to access the timer's register without clock. So I am not sure if >> ktime_get_mono_fast_ns() can work well for this case. > > I misread the code the same way before, but as Thomas Gleixner > pointed out, ktime_get_mono_fast_ns() will not call the clocksource > driver when timekeeping is suspended. See halt_fast_timekeeper().
Ah, I missed halt_fast_timekeeper() too, thanks for pointing it out. Now I think ktime_get_mono_fast_ns() can work for this case. Jason, could you drop the previous patch? I will respin v2 to use ktime_get_mono_fast_ns() as Arnd suggested. Thanks. -- Baolin.wang Best Regards
