FAILED: patch "[PATCH] hrtimer: Reset hrtimer cpu base proper on CPU hotplug" failed to apply to 3.18-stable tree

FAILED: patch "[PATCH] hrtimer: Reset hrtimer cpu base proper on CPU hotplug" failed to apply to 3.18-stable tree

[gregkh]

The patch below does not apply to the 3.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From d5421ea43d30701e03cadc56a38854c36a8b4433 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 26 Jan 2018 14:54:32 +0100
Subject: [PATCH] hrtimer: Reset hrtimer cpu base proper on CPU hotplug

The hrtimer interrupt code contains a hang detection and mitigation
mechanism, which prevents that a long delayed hrtimer interrupt causes a
continous retriggering of interrupts which prevent the system from making
progress. If a hang is detected then the timer hardware is programmed with
a certain delay into the future and a flag is set in the hrtimer cpu base
which prevents newly enqueued timers from reprogramming the timer hardware
prior to the chosen delay. The subsequent hrtimer interrupt after the delay
clears the flag and resumes normal operation.

If such a hang happens in the last hrtimer interrupt before a CPU is
unplugged then the hang_detected flag is set and stays that way when the
CPU is plugged in again. At that point the timer hardware is not armed and
it cannot be armed because the hang_detected flag is still active, so
nothing clears that flag. As a consequence the CPU does not receive hrtimer
interrupts and no timers expire on that CPU which results in RCU stalls and
other malfunctions.

Clear the flag along with some other less critical members of the hrtimer
cpu base to ensure starting from a clean state when a CPU is plugged in.

Thanks to Paul, Sebastian and Anna-Maria for their help to get down to the
root cause of that hard to reproduce heisenbug. Once understood it's
trivial and certainly justifies a brown paperbag.

Fixes: 41d2e4949377 ("hrtimer: Tune hrtimer_interrupt hang logic")
Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Sewior <bigeasy@linutronix.de>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801261447590.2067@nanos

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index d32520840fde..aa9d2a2b1210 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -655,7 +655,9 @@ static void hrtimer_reprogram(struct hrtimer *timer,
 static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base)
 {
 	base->expires_next = KTIME_MAX;
+	base->hang_detected = 0;
 	base->hres_active = 0;
+	base->next_timer = NULL;
 }
 
 /*
@@ -1589,6 +1591,7 @@ int hrtimers_prepare_cpu(unsigned int cpu)
 		timerqueue_init_head(&cpu_base->clock_base[i].active);
 	}
 
+	cpu_base->active_bases = 0;
 	cpu_base->cpu = cpu;
 	hrtimer_init_hres(cpu_base);
 	return 0;

[PATCH] hrtimer: Reset hrtimer cpu base proper on CPU hotplug

[Sebastian Andrzej Siewior]

From: Thomas Gleixner <tglx@linutronix.de>

commit d5421ea43d30701e03cadc56a38854c36a8b4433 upstream.

The hrtimer interrupt code contains a hang detection and mitigation
mechanism, which prevents that a long delayed hrtimer interrupt causes a
continous retriggering of interrupts which prevent the system from making
progress. If a hang is detected then the timer hardware is programmed with
a certain delay into the future and a flag is set in the hrtimer cpu base
which prevents newly enqueued timers from reprogramming the timer hardware
prior to the chosen delay. The subsequent hrtimer interrupt after the delay
clears the flag and resumes normal operation.

If such a hang happens in the last hrtimer interrupt before a CPU is
unplugged then the hang_detected flag is set and stays that way when the
CPU is plugged in again. At that point the timer hardware is not armed and
it cannot be armed because the hang_detected flag is still active, so
nothing clears that flag. As a consequence the CPU does not receive hrtimer
interrupts and no timers expire on that CPU which results in RCU stalls and
other malfunctions.

Clear the flag along with some other less critical members of the hrtimer
cpu base to ensure starting from a clean state when a CPU is plugged in.

Thanks to Paul, Sebastian and Anna-Maria for their help to get down to the
root cause of that hard to reproduce heisenbug. Once understood it's
trivial and certainly justifies a brown paperbag.

Fixes: 41d2e4949377 ("hrtimer: Tune hrtimer_interrupt hang logic")
Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Sewior <bigeasy@linutronix.de>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801261447590.2067@nanos
[bigeasy: backport to v3.18, drop ->next_timer it was introduced later]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/time/hrtimer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 210b84882935..e4c722437708 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -612,6 +612,7 @@ static int hrtimer_reprogram(struct hrtimer *timer,
 static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base)
 {
 	base->expires_next.tv64 = KTIME_MAX;
+	base->hang_detected = 0;
 	base->hres_active = 0;
 }
 
@@ -1632,6 +1633,7 @@ static void init_hrtimers_cpu(int cpu)
 		timerqueue_init_head(&cpu_base->clock_base[i].active);
 	}
 
+	cpu_base->active_bases = 0;
 	cpu_base->cpu = cpu;
 	hrtimer_init_hres(cpu_base);
 }
-- 
2.15.1

Re: [PATCH] hrtimer: Reset hrtimer cpu base proper on CPU hotplug

[Greg KH]

On Mon, Jan 29, 2018 at 03:20:32PM +0100, Sebastian Andrzej Siewior wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> commit d5421ea43d30701e03cadc56a38854c36a8b4433 upstream.
> 
> The hrtimer interrupt code contains a hang detection and mitigation
> mechanism, which prevents that a long delayed hrtimer interrupt causes a
> continous retriggering of interrupts which prevent the system from making
> progress. If a hang is detected then the timer hardware is programmed with
> a certain delay into the future and a flag is set in the hrtimer cpu base
> which prevents newly enqueued timers from reprogramming the timer hardware
> prior to the chosen delay. The subsequent hrtimer interrupt after the delay
> clears the flag and resumes normal operation.
> 
> If such a hang happens in the last hrtimer interrupt before a CPU is
> unplugged then the hang_detected flag is set and stays that way when the
> CPU is plugged in again. At that point the timer hardware is not armed and
> it cannot be armed because the hang_detected flag is still active, so
> nothing clears that flag. As a consequence the CPU does not receive hrtimer
> interrupts and no timers expire on that CPU which results in RCU stalls and
> other malfunctions.
> 
> Clear the flag along with some other less critical members of the hrtimer
> cpu base to ensure starting from a clean state when a CPU is plugged in.
> 
> Thanks to Paul, Sebastian and Anna-Maria for their help to get down to the
> root cause of that hard to reproduce heisenbug. Once understood it's
> trivial and certainly justifies a brown paperbag.
> 
> Fixes: 41d2e4949377 ("hrtimer: Tune hrtimer_interrupt hang logic")
> Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Sebastian Sewior <bigeasy@linutronix.de>
> Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
> Cc: stable@vger.kernel.org
> Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801261447590.2067@nanos
> [bigeasy: backport to v3.18, drop ->next_timer it was introduced later]

Thanks for the backport, now queued up.

greg k-h