[PATCH v4] time: Fix extra sleeptime injection when suspend fails

[PATCH v4] time: Fix extra sleeptime injection when suspend fails

[Mukesh Ojha]

Currently, there exists a corner case assuming when there is
only one clocksource e.g RTC, and system failed to go to
suspend mode. While resume rtc_resume() injects the sleeptime
as timekeeping_rtc_skipresume() returned 'false' (default value
of sleeptime_injected) due to which we can see mismatch in
timestamps.

This issue can also come in a system where more than one
clocksource are present and very first suspend fails.

Fix this by handling the sleeptime_injected flag properly.

Success case:
------------
                                        {sleeptime_injected=false}
rtc_suspend() => timekeeping_suspend() => timekeeping_resume() =>

(sleeptime injected)
 rtc_resume()

Failure case:
------------
         {failure in sleep path} {sleeptime_injected=false}
rtc_suspend()     =>          rtc_resume()

sleeptime injected again which was not required as the suspend failed)

Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
---
Changes in V4:
 * Changes as suggested by John
    - Changed the variable name from sleeptime_injected to suspend_timing_needed
    - Changed the boolean logic.
Changes in v3:
 * Updated commit subject and description.
 * Updated the patch as per the fix given by Thomas Gleixner.

Changes in v2:
 * Updated the commit text.
 * Removed extra variable and used the earlier static
   variable 'sleeptime_injected'.
 drivers/rtc/class.c       |  2 +-
 kernel/time/timekeeping.c | 29 ++++++++++++++++++++++-------
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index d37588f..ee455cc 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -102,7 +102,7 @@ static int rtc_resume(struct device *dev)
 	struct timespec64	sleep_time;
 	int err;
 
-	if (timekeeping_rtc_skipresume())
+	if (!timekeeping_rtc_skipresume())
 		return 0;
 
 	rtc_hctosys_ret = -ENODEV;
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4786df9..b25f771 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 false and is only set when a suspend reaches
+ * timekeeping_suspend(), timekeeping_resume() sets it to false 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 true and is used by the RTC resume code to decide
+ * whether sleeptime must be injected and if so the flag gets false then.
+ *
+ * If a suspend fails before reaching timekeeping_resume() then the flag
+ * stays false and prevents erroneous sleeptime injection.
+ */
+static bool suspend_timing_needed;
 
 /* Flag for if there is a persistent clock on this platform */
 static bool persistent_clock_exists;
@@ -1610,7 +1622,7 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
  */
 bool timekeeping_rtc_skipresume(void)
 {
-	return sleeptime_injected;
+	return suspend_timing_needed;
 }
 
 /**
@@ -1646,6 +1658,8 @@ void timekeeping_inject_sleeptime64(struct timespec64 *delta)
 	raw_spin_lock_irqsave(&timekeeper_lock, flags);
 	write_seqcount_begin(&tk_core.seq);
 
+	suspend_timing_needed = false;
+
 	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();
@@ -1701,13 +1714,13 @@ 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 = false;
 	} 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 = false;
 	}
 
-	if (sleeptime_injected)
+	if (!suspend_timing_needed)
 		__timekeeping_inject_sleeptime(tk, &ts_delta);
 
 	/* Re-base the last cycle value */
@@ -1743,6 +1756,8 @@ int timekeeping_suspend(void)
 	if (timekeeping_suspend_time.tv_sec || timekeeping_suspend_time.tv_nsec)
 		persistent_clock_exists = true;
 
+	suspend_timing_needed = true;
+
 	raw_spin_lock_irqsave(&timekeeper_lock, flags);
 	write_seqcount_begin(&tk_core.seq);
 	timekeeping_forward_now(tk);
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project

Re: [PATCH v4] time: Fix extra sleeptime injection when suspend fails

[Thomas Gleixner]

On Tue, 17 Jul 2018, Mukesh Ojha wrote:
> @@ -102,7 +102,7 @@ static int rtc_resume(struct device *dev)
>  	struct timespec64	sleep_time;
>  	int err;
>  
> -	if (timekeeping_rtc_skipresume())
> +	if (!timekeeping_rtc_skipresume())
>  		return 0;

That does not make any sense at all, really. 

>  /* Flag for if there is a persistent clock on this platform */
>  static bool persistent_clock_exists;
> @@ -1610,7 +1622,7 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
>   */
>  bool timekeeping_rtc_skipresume(void)
>  {
> -	return sleeptime_injected;
> +	return suspend_timing_needed;

Just make this !suspend_timing_needed and the function name and its return
value still makes sense.

> @@ -1701,13 +1714,13 @@ 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 = false;
>  	} 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 = false;
>  	}
>  
> -	if (sleeptime_injected)
> +	if (!suspend_timing_needed)
>  		__timekeeping_inject_sleeptime(tk, &ts_delta);

This reads odd as well. I'd rather keep a local variable inject_sleeptime
or such and set that in the code pathes above.

   	if (...) {
	   	...
		inject_sleeptime = true;
   	} else if (...) {
	   	...
		inject_sleeptime = true;
	}

	if (inject_sleeptime) {
		suspend_timing_needed = false;
		__timekeeping_inject_sleeptime();
	}

Hmm? Just blindly converting everything results in functional, but
nonsensical code. Think about what happens when you look at that stuff 6
month from now...

Thanks,

	tglx

Re: [PATCH v4] time: Fix extra sleeptime injection when suspend fails

[John Stultz]

On Mon, Jul 16, 2018 at 1:40 PM, Mukesh Ojha <mojha@codeaurora.org> wrote:
> Currently, there exists a corner case assuming when there is
> only one clocksource e.g RTC, and system failed to go to
> suspend mode. While resume rtc_resume() injects the sleeptime
> as timekeeping_rtc_skipresume() returned 'false' (default value
> of sleeptime_injected) due to which we can see mismatch in
> timestamps.
>
> This issue can also come in a system where more than one
> clocksource are present and very first suspend fails.
>
> Fix this by handling the sleeptime_injected flag properly.
>
> Success case:
> ------------
>                                         {sleeptime_injected=false}
> rtc_suspend() => timekeeping_suspend() => timekeeping_resume() =>
>
> (sleeptime injected)
>  rtc_resume()
>
> Failure case:
> ------------
>          {failure in sleep path} {sleeptime_injected=false}
> rtc_suspend()     =>          rtc_resume()
>
> sleeptime injected again which was not required as the suspend failed)
>
> Originally-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
> ---
> Changes in V4:
>  * Changes as suggested by John
>     - Changed the variable name from sleeptime_injected to suspend_timing_needed
>     - Changed the boolean logic.

Thanks so much for reworking and resending this again!


> diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
> index d37588f..ee455cc 100644
> --- a/drivers/rtc/class.c
> +++ b/drivers/rtc/class.c
> @@ -102,7 +102,7 @@ static int rtc_resume(struct device *dev)
>         struct timespec64       sleep_time;
>         int err;
>
> -       if (timekeeping_rtc_skipresume())
> +       if (!timekeeping_rtc_skipresume())


Hrm... So I'd have instead inverted the logic *in*
timekeeping_rtc_skipresume(), rather then here,  but this looks to be
close enough and I can fix that bit up.

Can you confirm you've validated this version of the patch resolves
the issue you reported?

thanks
-john

Re: [PATCH v4] time: Fix extra sleeptime injection when suspend fails

[Mukesh Ojha]

On 7/17/2018 2:20 AM, Thomas Gleixner wrote:
> On Tue, 17 Jul 2018, Mukesh Ojha wrote:
>> @@ -102,7 +102,7 @@ static int rtc_resume(struct device *dev)
>>   	struct timespec64	sleep_time;
>>   	int err;
>>   
>> -	if (timekeeping_rtc_skipresume())
>> +	if (!timekeeping_rtc_skipresume())
>>   		return 0;
> That does not make any sense at all, really.
>
>>   /* Flag for if there is a persistent clock on this platform */
>>   static bool persistent_clock_exists;
>> @@ -1610,7 +1622,7 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
>>    */
>>   bool timekeeping_rtc_skipresume(void)
>>   {
>> -	return sleeptime_injected;
>> +	return suspend_timing_needed;
> Just make this !suspend_timing_needed and the function name and its return
> value still makes sense.
>
>> @@ -1701,13 +1714,13 @@ 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 = false;
>>   	} 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 = false;
>>   	}
>>   
>> -	if (sleeptime_injected)
>> +	if (!suspend_timing_needed)
>>   		__timekeeping_inject_sleeptime(tk, &ts_delta);
> This reads odd as well. I'd rather keep a local variable inject_sleeptime
> or such and set that in the code pathes above.
>
>     	if (...) {
> 	   	...
> 		inject_sleeptime = true;
>     	} else if (...) {
> 	   	...
> 		inject_sleeptime = true;
> 	}
>
> 	if (inject_sleeptime) {
> 		suspend_timing_needed = false;
> 		__timekeeping_inject_sleeptime();
> 	}

Will do suggested change and send in v5.

Thanks.
>
> Hmm? Just blindly converting everything results in functional, but
> nonsensical code. Think about what happens when you look at that stuff 6
> month from now...
>
> Thanks,
>
> 	tglx
>

Re: [PATCH v4] time: Fix extra sleeptime injection when suspend fails

[Mukesh Ojha]

On 7/17/2018 2:31 AM, John Stultz wrote:
> On Mon, Jul 16, 2018 at 1:40 PM, Mukesh Ojha <mojha@codeaurora.org> wrote:
>> Currently, there exists a corner case assuming when there is
>> only one clocksource e.g RTC, and system failed to go to
>> suspend mode. While resume rtc_resume() injects the sleeptime
>> as timekeeping_rtc_skipresume() returned 'false' (default value
>> of sleeptime_injected) due to which we can see mismatch in
>> timestamps.
>>
>> This issue can also come in a system where more than one
>> clocksource are present and very first suspend fails.
>>
>> Fix this by handling the sleeptime_injected flag properly.
>>
>> Success case:
>> ------------
>>                                          {sleeptime_injected=false}
>> rtc_suspend() => timekeeping_suspend() => timekeeping_resume() =>
>>
>> (sleeptime injected)
>>   rtc_resume()
>>
>> Failure case:
>> ------------
>>           {failure in sleep path} {sleeptime_injected=false}
>> rtc_suspend()     =>          rtc_resume()
>>
>> sleeptime injected again which was not required as the suspend failed)
>>
>> Originally-by: Thomas Gleixner <tglx@linutronix.de>
>> Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
>> ---
>> Changes in V4:
>>   * Changes as suggested by John
>>      - Changed the variable name from sleeptime_injected to suspend_timing_needed
>>      - Changed the boolean logic.
> Thanks so much for reworking and resending this again!
>
>
>> diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
>> index d37588f..ee455cc 100644
>> --- a/drivers/rtc/class.c
>> +++ b/drivers/rtc/class.c
>> @@ -102,7 +102,7 @@ static int rtc_resume(struct device *dev)
>>          struct timespec64       sleep_time;
>>          int err;
>>
>> -       if (timekeeping_rtc_skipresume())
>> +       if (!timekeeping_rtc_skipresume())
>
> Hrm... So I'd have instead inverted the logic *in*
> timekeeping_rtc_skipresume(), rather then here,  but this looks to be
> close enough and I can fix that bit up.

Will take care of yours and Thomas comment in v5.

>
> Can you confirm you've validated this version of the patch resolves
> the issue you reported?
Yeah, I validated.

Thanks
Mukesh


>
> thanks
> -john