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From: Thomas Gleixner <tglx@linutronix.de>
To: linux-arm-kernel@lists.infradead.org
Subject: Re: Possible regression due to "hrtimer: Get rid of hrtimer softirq"
Date: Thu, 07 May 2015 12:35:59 +0000	[thread overview]
Message-ID: <alpine.DEB.2.11.1505071425520.4225@nanos> (raw)
In-Reply-To: <20150507111711.GA17448@verge.net.au>

On Thu, 7 May 2015, Simon Horman wrote:
> ------------[ cut here ]------------
> kernel BUG at kernel/irq_work.c:135!

  BUG_ON(!irqs_disabled());

So something enables interrupts in the periodic tick handling
machinery. Seems you have high resolution timers disabled, but nohz
enabled. And that code path has a local_irq_disable/enable pair which
causes havoc. Patch below.

Thanks,

	tglx

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 753c211f6195..812f7a3b9898 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -967,11 +967,9 @@ static void tick_nohz_switch_to_nohz(void)
 	if (!tick_nohz_enabled)
 		return;
 
-	local_irq_disable();
-	if (tick_switch_to_oneshot(tick_nohz_handler)) {
-		local_irq_enable();
+	if (tick_switch_to_oneshot(tick_nohz_handler))
 		return;
-	}
+
 	tick_nohz_active = 1;
 	ts->nohz_mode = NOHZ_MODE_LOWRES;
 
@@ -986,7 +984,6 @@ static void tick_nohz_switch_to_nohz(void)
 	hrtimer_forward_now(&ts->sched_timer, tick_period);
 	hrtimer_set_expires(&ts->sched_timer, next);
 	tick_program_event(next, 1);
-	local_irq_enable();
 }
 
 /*
@@ -1171,7 +1168,7 @@ void tick_oneshot_notify(void)
  * Called cyclic from the hrtimer softirq (driven by the timer
  * softirq) allow_nohz signals, that we can switch into low-res nohz
  * mode, because high resolution timers are disabled (either compile
- * or runtime).
+ * or runtime). Called with interrupts disabled.
  */
 int tick_check_oneshot_change(int allow_nohz)
 {





WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: Simon Horman <horms@verge.net.au>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Magnus Damm <magnus.damm@gmail.com>,
	linux-sh@vger.kernel.org,
	LAK <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: Possible regression due to "hrtimer: Get rid of hrtimer softirq"
Date: Thu, 7 May 2015 14:35:59 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1505071425520.4225@nanos> (raw)
In-Reply-To: <20150507111711.GA17448@verge.net.au>

On Thu, 7 May 2015, Simon Horman wrote:
> ------------[ cut here ]------------
> kernel BUG at kernel/irq_work.c:135!

  BUG_ON(!irqs_disabled());

So something enables interrupts in the periodic tick handling
machinery. Seems you have high resolution timers disabled, but nohz
enabled. And that code path has a local_irq_disable/enable pair which
causes havoc. Patch below.

Thanks,

	tglx

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 753c211f6195..812f7a3b9898 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -967,11 +967,9 @@ static void tick_nohz_switch_to_nohz(void)
 	if (!tick_nohz_enabled)
 		return;
 
-	local_irq_disable();
-	if (tick_switch_to_oneshot(tick_nohz_handler)) {
-		local_irq_enable();
+	if (tick_switch_to_oneshot(tick_nohz_handler))
 		return;
-	}
+
 	tick_nohz_active = 1;
 	ts->nohz_mode = NOHZ_MODE_LOWRES;
 
@@ -986,7 +984,6 @@ static void tick_nohz_switch_to_nohz(void)
 	hrtimer_forward_now(&ts->sched_timer, tick_period);
 	hrtimer_set_expires(&ts->sched_timer, next);
 	tick_program_event(next, 1);
-	local_irq_enable();
 }
 
 /*
@@ -1171,7 +1168,7 @@ void tick_oneshot_notify(void)
  * Called cyclic from the hrtimer softirq (driven by the timer
  * softirq) allow_nohz signals, that we can switch into low-res nohz
  * mode, because high resolution timers are disabled (either compile
- * or runtime).
+ * or runtime). Called with interrupts disabled.
  */
 int tick_check_oneshot_change(int allow_nohz)
 {





WARNING: multiple messages have this Message-ID (diff)
From: tglx@linutronix.de (Thomas Gleixner)
To: linux-arm-kernel@lists.infradead.org
Subject: Possible regression due to "hrtimer: Get rid of hrtimer softirq"
Date: Thu, 7 May 2015 14:35:59 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1505071425520.4225@nanos> (raw)
In-Reply-To: <20150507111711.GA17448@verge.net.au>

On Thu, 7 May 2015, Simon Horman wrote:
> ------------[ cut here ]------------
> kernel BUG at kernel/irq_work.c:135!

  BUG_ON(!irqs_disabled());

So something enables interrupts in the periodic tick handling
machinery. Seems you have high resolution timers disabled, but nohz
enabled. And that code path has a local_irq_disable/enable pair which
causes havoc. Patch below.

Thanks,

	tglx

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 753c211f6195..812f7a3b9898 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -967,11 +967,9 @@ static void tick_nohz_switch_to_nohz(void)
 	if (!tick_nohz_enabled)
 		return;
 
-	local_irq_disable();
-	if (tick_switch_to_oneshot(tick_nohz_handler)) {
-		local_irq_enable();
+	if (tick_switch_to_oneshot(tick_nohz_handler))
 		return;
-	}
+
 	tick_nohz_active = 1;
 	ts->nohz_mode = NOHZ_MODE_LOWRES;
 
@@ -986,7 +984,6 @@ static void tick_nohz_switch_to_nohz(void)
 	hrtimer_forward_now(&ts->sched_timer, tick_period);
 	hrtimer_set_expires(&ts->sched_timer, next);
 	tick_program_event(next, 1);
-	local_irq_enable();
 }
 
 /*
@@ -1171,7 +1168,7 @@ void tick_oneshot_notify(void)
  * Called cyclic from the hrtimer softirq (driven by the timer
  * softirq) allow_nohz signals, that we can switch into low-res nohz
  * mode, because high resolution timers are disabled (either compile
- * or runtime).
+ * or runtime). Called with interrupts disabled.
  */
 int tick_check_oneshot_change(int allow_nohz)
 {

  reply	other threads:[~2015-05-07 12:35 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-07 11:17 Possible regression due to "hrtimer: Get rid of hrtimer softirq" Simon Horman
2015-05-07 11:17 ` Simon Horman
2015-05-07 11:17 ` Simon Horman
2015-05-07 12:35 ` Thomas Gleixner [this message]
2015-05-07 12:35   ` Thomas Gleixner
2015-05-07 12:35   ` Thomas Gleixner
2015-05-07 13:25   ` Simon Horman
2015-05-07 13:25     ` Simon Horman
2015-05-07 13:25     ` Simon Horman
2015-05-08 17:14     ` Kevin Hilman
2015-05-08 17:14       ` Kevin Hilman
2015-05-08 17:14       ` Kevin Hilman
2015-05-08  9:25   ` [tip:timers/core] nohz: Fix !HIGH_RES_TIMERS hang tip-bot for Thomas Gleixner

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