linux-kernel - Re: [PATCH 16/20] sched/idle: Use explicit broadcast oneshot control function

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Date:	Tue, 28 Apr 2015 15:31:54 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 16/20] sched/idle: Use explicit broadcast oneshot control function

On Tuesday, April 28, 2015 02:37:10 PM Linus Walleij wrote:
> On Tue, Apr 28, 2015 at 2:19 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> > Sudeep:
> >> At-least I observed issue only when I am using hardware broadcast timer.
> >> It doesn't hang when I am using hrtimer as broadcast timer in which case
> >> one of the cpu will be not enter deeper idle states that lose timer.
> >> I will rerun on v4.1-rc1 and post the complete log.
> >
> > So the bug here is that cpuidle_enter() enables interrupts, so the
> > assumption about them being not enabled made by
> > tick_broadcast_oneshot_control() is actually not valid.
> >
> > It looks like we need to acquire the clockevents_lock at least in this
> > particular case.  Let me see where to put it and I'll send a patch for
> > testing.
> 
> Aha that looks very much like it. Put me on the patch and I'll
> take it for a spin.

OK, so something like the below for starters (the _irqsave variant is used to
avoid adding one more WARN_ON(irqs_disabled()) in there).

I haven't tested it, but then I can't reproduce the original issue in the
first place.

---
 include/linux/clockchips.h |    2 ++
 kernel/sched/idle.c        |    2 +-
 kernel/time/clockevents.c  |   15 +++++++++++++++
 3 files changed, 18 insertions(+), 1 deletion(-)

Index: linux-pm/include/linux/clockchips.h
===================================================================
--- linux-pm.orig/include/linux/clockchips.h
+++ linux-pm/include/linux/clockchips.h
@@ -198,9 +198,11 @@ extern int tick_receive_broadcast(void);
 # if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT)
 extern void tick_setup_hrtimer_broadcast(void);
 extern int tick_check_broadcast_expired(void);
+extern void tick_broadcast_exit_idle(void);
 # else
 static inline int tick_check_broadcast_expired(void) { return 0; }
 static inline void tick_setup_hrtimer_broadcast(void) { }
+static inline void tick_broadcast_exit_idle(void) { }
 # endif
 
 extern int clockevents_notify(unsigned long reason, void *arg);
Index: linux-pm/kernel/time/clockevents.c
===================================================================
--- linux-pm.orig/kernel/time/clockevents.c
+++ linux-pm/kernel/time/clockevents.c
@@ -735,6 +735,21 @@ static ssize_t sysfs_unbind_tick_dev(str
 static DEVICE_ATTR(unbind_device, 0200, NULL, sysfs_unbind_tick_dev);
 
 #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
+/**
+ * tick_broadcast_exit_idle - Broadcast oneshot mode exit for the idle loop.
+ *
+ * The idle loop exits the broadcast oneshot mode with interrupts enabled, so
+ * clockevents_lock needs to be acquired around that.
+ */
+void tick_broadcast_exit_idle(void)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&clockevents_lock, flags);
+	tick_broadcast_exit();
+	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
+}
+
 static struct device tick_bc_dev = {
 	.init_name	= "broadcast",
 	.id		= 0,
Index: linux-pm/kernel/sched/idle.c
===================================================================
--- linux-pm.orig/kernel/sched/idle.c
+++ linux-pm/kernel/sched/idle.c
@@ -175,7 +175,7 @@ static void cpuidle_idle_call(void)
 	idle_set_state(this_rq(), NULL);
 
 	if (broadcast)
-		tick_broadcast_exit();
+		tick_broadcast_exit_idle();
 
 	/*
 	 * Give the governor an opportunity to reflect on the outcome

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