linux-kernel - Re: [PATCH][RFC v4] timekeeping: ignore the bogus sleep time if pm

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Date:   Sat, 27 Aug 2016 15:08:56 +0800
From:   Xunlei Pang <xpang@...hat.com>
To:     Chen Yu <yu.c.chen@...el.com>, linux-pm@...r.kernel.org
Cc:     Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
        x86@...nel.org, "Rafael J . Wysocki" <rjw@...ysocki.net>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Xunlei Pang <xlpang@...hat.com>,
        Zhang Rui <rui.zhang@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC v4] timekeeping: ignore the bogus sleep time if
 pm_trace is enabled

On 2016/08/18 at 18:43, Chen Yu wrote:
> Previously we encountered some memory overflow issues due to
> the bogus sleep time brought by inconsistent rtc, which is
> triggered when pm_trace is enabled, please refer to:
> https://patchwork.kernel.org/patch/9286365/
> It's improper in the first place to call __timekeeping_inject_sleeptime()
> in case that pm_trace is enabled simply because that "hash" time value
> will wreckage the timekeeping subsystem.
>
> So this patch ignores the sleep time if pm_trace is enabled in
> the following situation:
> 1. rtc is used as persist clock to compensate for sleep time,
>    (because system does not have a nonstop clocksource) or
> 2. rtc is used to calculate the sleep time in rtc_resume.
>
> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> Cc: John Stultz <john.stultz@...aro.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Xunlei Pang <xlpang@...hat.com>
> Cc: Zhang Rui <rui.zhang@...el.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-pm@...r.kernel.org
> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Reported-by: Janek Kozicki <cosurgi@...il.com>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
>  arch/x86/kernel/rtc.c     |  7 +++++++
>  kernel/time/timekeeping.c | 14 +++++++++++++-
>  2 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
> index 79c6311c..6039138 100644
> --- a/arch/x86/kernel/rtc.c
> +++ b/arch/x86/kernel/rtc.c
> @@ -8,6 +8,7 @@
>  #include <linux/export.h>
>  #include <linux/pnp.h>
>  #include <linux/of.h>
> +#include <linux/pm-trace.h>
>  
>  #include <asm/vsyscall.h>
>  #include <asm/x86_init.h>
> @@ -146,6 +147,12 @@ void read_persistent_clock(struct timespec *ts)
>  	x86_platform.get_wallclock(ts);
>  }
>  
> +bool persistent_clock_is_usable(void)
> +{
> +	/* Unusable if pm_trace is enabled. */
> +	return !((x86_platform.get_wallclock == mach_get_cmos_time) &&
> +		 pm_trace_is_enabled());
> +}
>  
>  static struct resource rtc_resources[] = {
>  	[0] = {
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 3b65746..3122bd2b 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -23,6 +23,7 @@
>  #include <linux/stop_machine.h>
>  #include <linux/pvclock_gtod.h>
>  #include <linux/compiler.h>
> +#include <linux/pm-trace.h>
>  
>  #include "tick-internal.h"
>  #include "ntp_internal.h"
> @@ -1450,6 +1451,11 @@ void __weak read_boot_clock64(struct timespec64 *ts)
>  	ts->tv_nsec = 0;
>  }
>  
> +bool __weak persistent_clock_is_usable(void)
> +{
> +	return true;
> +}
> +

I suddenly think of a way to avoid adding this ugly __weak auxiliary function.

Add a special treatment for read_persistent_clock() in arch/x86/kernel/rtc.c as follows,
void read_persistent_clock(struct timespec *ts)
{
    x86_platform.get_wallclock(ts);

    /* Make rtc-based persistent clock unusable if pm_trace is enabled. */
    if (pm_trace_is_enabled() &&
        x86_platform.get_wallclock == mach_get_cmos_time) {
        ts->tv_sec = 0;
        ts->tv_nsec = 0;
    }
}

In this way, we can avoid the touch of timekeeping core, after all ptrace is currently x86-specific.

What do you think?

Regards,
Xunlei

>  /* Flag for if timekeeping_resume() has injected sleeptime */
>  static bool sleeptime_injected;
>  
> @@ -1551,7 +1557,7 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
>   */
>  bool timekeeping_rtc_skipresume(void)
>  {
> -	return sleeptime_injected;
> +	return sleeptime_injected || pm_trace_is_enabled();
>  }
>  
>  /**
> @@ -1662,6 +1668,12 @@ void timekeeping_resume(void)
>  	} else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {
>  		ts_delta = timespec64_sub(ts_new, timekeeping_suspend_time);
>  		sleeptime_injected = true;
> +		/*
> +		 * If rtc is used as persist clock thus it
> +		 * would be bogus when pm_trace is enabled.
> +		 */
> +		if (!persistent_clock_is_usable())
> +			sleeptime_injected = false;
>  	}
>  
>  	if (sleeptime_injected)