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.stu...@linaro.org> wrote:
On Mon, Jul 16, 2018 at 9:17 AM, Mukesh Ojha <mo...@codeaurora.org> wrote:
On 7/13/2018 10:50 PM, John Stultz wrote:
On Fri, Jul 13, 2018 at 12:13 AM, Mukesh Ojha <mo...@codeaurora.org>
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