linux-kernel - [tip:timers/urgent] timers/sched_clock: Prevent generic sched_clock wrap caused by tick

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Date:   Thu, 18 Apr 2019 05:40:58 -0700
From:   tip-bot for Chang-An Chen <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     stanley.chu@...iatek.com, fweisbec@...il.com, cminyard@...sta.com,
        linux-mediatek@...ts.infradead.org, tglx@...utronix.de,
        linux-arm-kernel@...ts.infradead.org, chang-an.chen@...iatek.com,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        kuohong.wang@...iatek.com, freddy.hsin@...iatek.com,
        john.stultz@...aro.org, matthias.bgg@...il.com, hpa@...or.com,
        keescook@...omium.org
Subject: [tip:timers/urgent] timers/sched_clock: Prevent generic sched_clock
 wrap caused by tick_freeze()

Commit-ID:  3f2552f7e9c5abef2775c53f7af66532f8bf65bc
Gitweb:     https://git.kernel.org/tip/3f2552f7e9c5abef2775c53f7af66532f8bf65bc
Author:     Chang-An Chen <chang-an.chen@...iatek.com>
AuthorDate: Fri, 29 Mar 2019 10:59:09 +0800
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 18 Apr 2019 14:34:53 +0200

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

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().

Fixes: 124cf9117c5f (PM / sleep: Make it possible to quiesce timers during suspend-to-idle)
Signed-off-by: Chang-An Chen <chang-an.chen@...iatek.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Matthias Brugger <matthias.bgg@...il.com>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Corey Minyard <cminyard@...sta.com>
Cc: <linux-mediatek@...ts.infradead.org>
Cc: <linux-arm-kernel@...ts.infradead.org>
Cc: Stanley Chu <stanley.chu@...iatek.com>
Cc: <kuohong.wang@...iatek.com>
Cc: <freddy.hsin@...iatek.com>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/1553828349-8914-1-git-send-email-chang-an.chen@mediatek.com
---
 kernel/time/sched_clock.c | 4 ++--
 kernel/time/tick-common.c | 2 ++
 kernel/time/timekeeping.h | 7 +++++++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index 094b82ca95e5..930113b9799a 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -272,7 +272,7 @@ static u64 notrace suspended_sched_clock_read(void)
 	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];
 
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 529143b4c8d2..df401463a191 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -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);
diff --git a/kernel/time/timekeeping.h b/kernel/time/timekeeping.h
index 7a9b4eb7a1d5..141ab3ab0354 100644
--- a/kernel/time/timekeeping.h
+++ b/kernel/time/timekeeping.h
@@ -14,6 +14,13 @@ extern u64 timekeeping_max_deferment(void);
 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);