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

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Date:   Tue, 17 Jul 2018 00:00:26 +0530
From:   Mukesh Ojha <mojha@...eaurora.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>, gkohli@...eaurora.org,
        cpandya@...eaurora.org, neeraju@...eaurora.org,
        Baolin Wang <baolin.wang@...aro.org>
Subject: Re: [PATCH v3] time: Fix incorrect sleeptime injection when suspend
 fails



On 7/16/2018 10:44 PM, John Stultz wrote:
> On Mon, Jul 16, 2018 at 9:30 AM, John Stultz <john.stultz@...aro.org> wrote:
>> On Mon, Jul 16, 2018 at 9:17 AM, Mukesh Ojha <mojha@...eaurora.org> wrote:
>>> On 7/13/2018 10:50 PM, John Stultz wrote:
>>>> On Fri, Jul 13, 2018 at 12:13 AM, Mukesh Ojha <mojha@...eaurora.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