Re: [PATCH v3] time: Fix incorrect sleeptime injection when suspend fails

[Mukesh Ojha]

On 7/16/2018 10:44 PM, John Stultz wrote:
> On Mon, Jul 16, 2018 at 9:30 AM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
> > On Mon, Jul 16, 2018 at 9:17 AM, Mukesh Ojha <mojha@xxxxxxxxxxxxxx> wrote:
> > > On 7/13/2018 10:50 PM, John Stultz wrote:
> > > > On Fri, Jul 13, 2018 at 12:13 AM, Mukesh Ojha <mojha@xxxxxxxxxxxxxx>
> > > > > On 7/11/2018 1:43 AM, John Stultz wrote:
> > > > > > I worry this upside-down logic is too subtle to be easily reasoned
> > > > > > about, and will just lead to future mistakes.
> > > > > >
> > > > > > Can we instead call this "suspend_timing_needed" and only set it to
> > > > > > true when we don't inject any sleep time on resume?
> > > > >
> > > > > I did not get your point "only set it to true when we don't inject any
> > > > > sleep
> > > > > time on resume? "
> > > > > How do we know  this ?
> > > > > This question itself depends on the "sleeptime_injected" if it is true
> > > > > means
> > > > > no need to inject else need to inject.
> > > > >
> > > > > Also, we need to make this variable back and forth true, false; suspends
> > > > > path ensures it to make it false.
> > > > So yea, I'm not saying logically the code is really any different,
> > > > this is more of a naming nit. So instead of having a variable that is
> > > > always on that we occasionally turn off, lets invert the naming and
> > > > have it be a flag that we occasionally turn on.
> > >
> > > I understand your concern about the name of the variable will be misleading.
> > > But the changing Boolean state would not solve the actual issue.
> > >
> > > If i understand you correctly you meant below code
> > >
> > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> > > index 32ae9ae..becc5bd 100644
> > > --- a/kernel/time/timekeeping.c
> > > +++ b/kernel/time/timekeeping.c
> > > @@ -1523,7 +1523,7 @@ void __weak read_boot_clock64(struct timespec64 *ts)
> > >    * If a suspend fails before reaching timekeeping_resume() then the flag
> > >    * stays true and prevents erroneous sleeptime injection.
> > >    */
> > > -static bool sleeptime_injected = true;
> > > +static bool suspend_timing_needed;
> > >
> > >   /* Flag for if there is a persistent clock on this platform */
> > >   static bool persistent_clock_exists;
> > > @@ -1658,7 +1658,7 @@ void timekeeping_inject_sleeptime64(struct timespec64
> > > *delta)
> > >          raw_spin_lock_irqsave(&timekeeper_lock, flags);
> > >          write_seqcount_begin(&tk_core.seq);
> > >
> > > -       sleeptime_injected = true;
> > > +       suspend_timing_needed = false;
> > >
> > >          timekeeping_forward_now(tk);
> > >
> > > @@ -1714,10 +1714,10 @@ void timekeeping_resume(void)
> > >                                                tk->tkr_mono.mask);
> > >                  nsec = mul_u64_u32_shr(cyc_delta, clock->mult,
> > > clock->shift);
> > >                  ts_delta = ns_to_timespec64(nsec);
> > > -               sleeptime_injected = true;
> > > +               suspend_timing_needed = true;
> > >          } else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) >
> > > 0) {
> > >                  ts_delta = timespec64_sub(ts_new, timekeeping_suspend_time);
> > > -               sleeptime_injected = true;
> > > +               suspend_timing_needed = true;
> > >          }
> > No no... This part is wrong. We only set suspend_timing_needed if we
> > *didn't* calculate the suspend time in timekeeping_resume.
> >
> > You have to invert all the boolean logic for it to be equivalent.
> ...
> > >    <sleeptime injection happens here>
> >
> > So, I think with the logic bug above it will work out properly, but
> > let me know if I'm still missing something.

Please give it thought to a case where very first suspend fails with 
your logic.
If i am not able to get your thought, please write a patch.

-Mukesh

> Sorry, I meant "with the logic bug above fixed it will work out".
>
> thanks
> -john