This is a note to let you know that I've just added the patch titled
tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem
to the 5.10-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:
tick-nohz-fix-cpu_is_hotpluggable-by-checking-with-nohz-subsystem.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 58d7668242647e661a20efe065519abd6454287e Mon Sep 17 00:00:00 2001
From: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>
Date: Tue, 24 Jan 2023 17:31:26 +0000
Subject: tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem
From: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
commit 58d7668242647e661a20efe065519abd6454287e upstream.
For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined.
However, cpu_is_hotpluggable() still returns true for those CPUs. This causes
torture tests that do offlining to end up trying to offline this CPU causing
test failures. Such failure happens on all architectures.
Fix the repeated error messages thrown by this (even if the hotplug errors are
harmless) by asking the opinion of the nohz subsystem on whether the CPU can be
hotplugged.
[ Apply Frederic Weisbecker feedback on refactoring tick_nohz_cpu_down(). ]
For drivers/base/ portion:
Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Acked-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Zhouyi Zhou <zhouzhouyi@xxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: rcu <rcu@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 2987557f52b9 ("driver-core/cpu: Expose hotpluggability to the rest of the kernel")
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/base/cpu.c | 3 ++-
include/linux/tick.h | 2 ++
kernel/time/tick-sched.c | 11 ++++++++---
3 files changed, 12 insertions(+), 4 deletions(-)
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -489,7 +489,8 @@ static const struct attribute_group *cpu
bool cpu_is_hotpluggable(unsigned cpu)
{
struct device *dev = get_cpu_device(cpu);
- return dev && container_of(dev, struct cpu, dev)->hotpluggable;
+ return dev && container_of(dev, struct cpu, dev)->hotpluggable
+ && tick_nohz_cpu_hotpluggable(cpu);
}
EXPORT_SYMBOL_GPL(cpu_is_hotpluggable);
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -211,6 +211,7 @@ extern void tick_nohz_dep_set_signal(str
enum tick_dep_bits bit);
extern void tick_nohz_dep_clear_signal(struct signal_struct *signal,
enum tick_dep_bits bit);
+extern bool tick_nohz_cpu_hotpluggable(unsigned int cpu);
/*
* The below are tick_nohz_[set,clear]_dep() wrappers that optimize off-cases
@@ -275,6 +276,7 @@ static inline void tick_nohz_full_add_cp
static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { }
+static inline bool tick_nohz_cpu_hotpluggable(unsigned int cpu) { return true; }
static inline void tick_dep_set(enum tick_dep_bits bit) { }
static inline void tick_dep_clear(enum tick_dep_bits bit) { }
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -426,7 +426,7 @@ void __init tick_nohz_full_setup(cpumask
tick_nohz_full_running = true;
}
-static int tick_nohz_cpu_down(unsigned int cpu)
+bool tick_nohz_cpu_hotpluggable(unsigned int cpu)
{
/*
* The tick_do_timer_cpu CPU handles housekeeping duty (unbound
@@ -434,8 +434,13 @@ static int tick_nohz_cpu_down(unsigned i
* CPUs. It must remain online when nohz full is enabled.
*/
if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
- return -EBUSY;
- return 0;
+ return false;
+ return true;
+}
+
+static int tick_nohz_cpu_down(unsigned int cpu)
+{
+ return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY;
}
void __init tick_nohz_init(void)
Patches currently in stable-queue which might be from joel@xxxxxxxxxxxxxxxxx are
queue-5.10/kheaders-use-array-declaration-instead-of-char.patch
queue-5.10/tick-nohz-fix-cpu_is_hotpluggable-by-checking-with-nohz-subsystem.patch
