lkml.org 
[lkml]   [2018]   [Jun]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH v2] time: Fix sleeptime injection for non-stop clocksource & persistent clock
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.

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;

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

\
 
 \ /
  Last update: 2018-06-22 23:27    [W:0.110 / U:0.672 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site