lkml.org 
[lkml]   [2018]   [Jun]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2] time: Fix sleeptime injection for non-stop clocksource & persistent clock
From
Date
Hi Thomas,

Thanks you very much for your time and reply.


On 6/23/2018 2:57 AM, Thomas Gleixner wrote:
> On Wed, 30 May 2018, Mukesh Ojha wrote:
>> Currently, for both non-stop clocksource and persistent clock
>> there is a corner case, when a driver failed to go suspend mode.
>> rtc_resume() injects the sleeptime as timekeeping_rtc_skipresume()
>> returned 'false'(sleeptime_injected=false) due to which we can
>> see mismatch in timestamps between system clock and other timers.
>>
>> Fix this by updating sleeptime_injected=true for both non-stop
>> clocksource and persistent clock.
>>
>> Success case:
>> ------------
>> {sleeptime_injected=true}
>> rtc_suspend() => timekeeping_suspend() => timekeeping_resume() =>
>> rtc_resume()
>>
>> Failure case:
>> ------------
>> {failure in sleep path} {sleeptime_injected=false}
>> rtc_suspend() => rtc_resume()
> I can see the problem.
>
>> Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
>> ---
>> Changes in v2:
>> * Updated the commit text.
>> * Removed extra variable and used the earlier static
>> variable 'sleeptime_injected'.
>>
>> kernel/time/timekeeping.c | 11 +++++++++++
>> 1 file changed, 11 insertions(+)
>>
>> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
>> index 49cbcee..2754c1b 100644
>> --- a/kernel/time/timekeeping.c
>> +++ b/kernel/time/timekeeping.c
>> @@ -1610,6 +1610,17 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
>> */
>> bool timekeeping_rtc_skipresume(void)
>> {
>> + struct timekeeper *tk = &tk_core.timekeeper;
>> + /*
>> + * This is to ensure that we don't end up injecting
>> + * the sleeptime via rtc_resume() for non-stop clocksource
>> + * when we fail to sleep.
>> + */
>> + if (!sleeptime_injected)
>> + sleeptime_injected = ((tk->tkr_mono.clock->flags &
>> + CLOCK_SOURCE_SUSPEND_NONSTOP) ||
>> + (persistent_clock_exists)) ? true : false;
> But this is really a horrible hack. The right thing to do is to keep track
> whether timekeeping_suspend() has been reached in the first place. There is
> a very simple way to do that. Uncompiled and completely untested patch
> below, but you get the idea.

Yeah, missed completely the fact that the issue can also come where only
clocksource is RTC.
> Thanks,
>
> tglx
>
> 8<-------------------
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 4786df904c22..32ae9aea61c3 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1510,8 +1510,20 @@ void __weak read_boot_clock64(struct timespec64 *ts)
> ts->tv_nsec = 0;
> }
>
> -/* Flag for if timekeeping_resume() has injected sleeptime */
> -static bool sleeptime_injected;
> +/*
> + * Flag reflecting whether timekeeping_resume() has injected sleeptime.
> + *
> + * The flag starts of true and is only cleared when a suspend reaches
> + * timekeeping_suspend(), timekeeping_resume() sets it when the timekeeper
> + * clocksource is not stopping across suspend and has been used to update
> + * sleep time. If the timekeeper clocksource has stopped then the flag
> + * stays false and is used by the RTC resume code to decide whether sleep
> + * time must be injected and if so the flag gets set then.
> + *
> + * If a suspend fails before reaching timekeeping_resume() then the flag
> + * stays true and prevents erroneous sleeptime injection.
> + */
> +static bool sleeptime_injected = true;

This will prevent first sleep failure.

>
> /* Flag for if there is a persistent clock on this platform */
> static bool persistent_clock_exists;
> @@ -1646,6 +1658,8 @@ void timekeeping_inject_sleeptime64(struct timespec64 *delta)
> raw_spin_lock_irqsave(&timekeeper_lock, flags);
> write_seqcount_begin(&tk_core.seq);
>
> + sleeptime_injected = true;

This will prevent further extra sleeptime injection if sleep fails
(valid for RTC only).
Looks good!

> +
> timekeeping_forward_now(tk);
>
> __timekeeping_inject_sleeptime(tk, delta);
> @@ -1671,7 +1685,6 @@ void timekeeping_resume(void)
> struct timespec64 ts_new, ts_delta;
> u64 cycle_now;
>
> - sleeptime_injected = false;
> read_persistent_clock64(&ts_new);
>
> clockevents_resume();
> @@ -1743,6 +1756,8 @@ int timekeeping_suspend(void)
> if (timekeeping_suspend_time.tv_sec || timekeeping_suspend_time.tv_nsec)
> persistent_clock_exists = true;
>
> + sleeptime_injected = false;

I did not get the exact valid point of moving it from
`timekeeping_suspend` to `timekeeping_resume`.
Although it will not have any side effect.

> +
> raw_spin_lock_irqsave(&timekeeper_lock, flags);
> write_seqcount_begin(&tk_core.seq);
> timekeeping_forward_now(tk);
>

Thanks for the change;  will check and update.

Cheers,
Mukesh

\
 
 \ /
  Last update: 2018-06-25 16:39    [W:0.089 / U:22.996 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site