Hi John,
Thanks for your response
Please find my comments inline.
On 7/11/2018 1:43 AM, John Stultz wrote:
On Fri, Jul 6, 2018 at 6:17 AM, Mukesh Ojha <[email protected]> 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 `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 <[email protected]>
Signed-off-by: Mukesh Ojha <[email protected]>
---
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'.
kernel/time/timekeeping.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4786df9..32ae9ae 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;
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.
Just to add here there are already two path where `sleeptime_injected`
set to true one from
NON-stop clocksource and other from persistant clock and the RTC one was
missing, so we are adding
with this patch.
Cheers,
-Mukesh
