Patch "timers/sched_clock: Prevent generic sched_clock wrap caused by tick_freeze()" has been added to the 5.0-stable tree

This is a note to let you know that I've just added the patch titled

timers/sched_clock: Prevent generic sched_clock wrap caused by tick_freeze()

to the 5.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
timers-sched_clock-prevent-generic-sched_clock-wrap-caused-by-tick_freeze.patch
and it can be found in the queue-5.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Chang-An Chen <[email protected]>
Date: Fri, 29 Mar 2019 10:59:09 +0800
Subject: timers/sched_clock: Prevent generic sched_clock wrap caused by tick_freeze()

From: Chang-An Chen <[email protected]>

commit 3f2552f7e9c5abef2775c53f7af66532f8bf65bc upstream.

tick_freeze() introduced by suspend-to-idle in commit 124cf9117c5f ("PM /
sleep: Make it possible to quiesce timers during suspend-to-idle") uses timekeeping_suspend() instead of syscore_suspend() during suspend-to-idle. As a consequence generic sched_clock will keep going because sched_clock_suspend() and sched_clock_resume() are not invoked during suspend-to-idle which can result in a generic sched_clock wrap.

On a ARM system with suspend-to-idle enabled, sched_clock is registered as "56 bits at 13MHz, resolution 76ns, wraps every 4398046511101ns", which means the real wrapping duration is 8796093022202ns.

[  134.551779] suspend-to-idle suspend (timekeeping_suspend())
[ 1204.912239] suspend-to-idle resume (timekeeping_resume())
......
[ 1206.912239] suspend-to-idle suspend (timekeeping_suspend())
[ 5880.502807] suspend-to-idle resume (timekeeping_resume())
......
[ 6000.403724] suspend-to-idle suspend (timekeeping_suspend())
[ 8035.753167] suspend-to-idle resume  (timekeeping_resume())
......
[ 8795.786684] (2)[321:charger_thread]......
[ 8795.788387] (2)[321:charger_thread]......
[    0.057226] (0)[0:swapper/0]......
[    0.061447] (2)[0:swapper/2]......

sched_clock was not stopped during suspend-to-idle, and sched_clock_poll hrtimer was not expired because timekeeping_suspend() was invoked during suspend-to-idle. It makes sched_clock wrap at kernel time 8796s.

To prevent this, invoke sched_clock_suspend() and sched_clock_resume() in tick_freeze() together with timekeeping_suspend() and timekeeping_resume().

---
 kernel/time/sched_clock.c |    4 ++--
 kernel/time/tick-common.c |    2 ++
 kernel/time/timekeeping.h |    7 +++++++
 3 files changed, 11 insertions(+), 2 deletions(-)

@@ -272,7 +272,7 @@ static u64 notrace suspended_sched_clock
 	return cd.read_data[seq & 1].epoch_cyc;
 }
 
-static int sched_clock_suspend(void)
+int sched_clock_suspend(void)
 {
 	struct clock_read_data *rd = &cd.read_data[0];
 

@@ -283,7 +283,7 @@ static int sched_clock_suspend(void)
 	return 0;
 }
 
-static void sched_clock_resume(void)
+void sched_clock_resume(void)
 {
 	struct clock_read_data *rd = &cd.read_data[0];
 

@@ -487,6 +487,7 @@ void tick_freeze(void)
 		trace_suspend_resume(TPS("timekeeping_freeze"),
 				     smp_processor_id(), true);
 		system_state = SYSTEM_SUSPEND;
+		sched_clock_suspend();
 		timekeeping_suspend();
 	} else {
 		tick_suspend_local();

@@ -510,6 +511,7 @@ void tick_unfreeze(void)
 
 	if (tick_freeze_depth == num_online_cpus()) {
 		timekeeping_resume();
+		sched_clock_resume();
 		system_state = SYSTEM_RUNNING;
 		trace_suspend_resume(TPS("timekeeping_freeze"),
 				     smp_processor_id(), false);

@@ -14,6 +14,13 @@ extern u64 timekeeping_max_deferment(voi
 extern void timekeeping_warp_clock(void);
 extern int timekeeping_suspend(void);
 extern void timekeeping_resume(void);
+#ifdef CONFIG_GENERIC_SCHED_CLOCK
+extern int sched_clock_suspend(void);
+extern void sched_clock_resume(void);
+#else
+static inline int sched_clock_suspend(void) { return 0; }
+static inline void sched_clock_resume(void) { }
+#endif
 
 extern void do_timer(unsigned long ticks);
 extern void update_wall_time(void);

Patches currently in stable-queue which might be from [email protected] are

queue-5.0/timers-sched_clock-prevent-generic-sched_clock-wrap-caused-by-tick_freeze.patch