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

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Message-ID: <CALAqxLXN9=KgGpG+qexBesn5A2OyszyyzatkP5z_wg1GbcMzQA@mail.gmail.com>
Date:   Mon, 16 Jul 2018 10:14:19 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Mukesh Ojha <mojha@...eaurora.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 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.

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

thanks
-john