1 files changed, 101 insertions, 0 deletions
diff --git a/debian/patches-rt/0115-hotplug-Lightweight-get-online-cpus.patch b/debian/patches-rt/0115-hotplug-Lightweight-get-online-cpus.patch
new file mode 100644
index 000000000..5561bbcf7
--- /dev/null
+++ b/debian/patches-rt/0115-hotplug-Lightweight-get-online-cpus.patch
@@ -0,0 +1,101 @@
+From bf07bc52ad387c3cec5179aac1a8a08bfe0e24f7 Mon Sep 17 00:00:00 2001
+From: Thomas Gleixner <tglx@linutronix.de>
+Date: Wed, 15 Jun 2011 12:36:06 +0200
+Subject: [PATCH 115/347] hotplug: Lightweight get online cpus
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz
+
+get_online_cpus() is a heavy weight function which involves a global
+mutex. migrate_disable() wants a simpler construct which prevents only
+a CPU from going doing while a task is in a migrate disabled section.
+
+Implement a per cpu lockless mechanism, which serializes only in the
+real unplug case on a global mutex. That serialization affects only
+tasks on the cpu which should be brought down.
+
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+---
+ include/linux/cpu.h |  5 +++++
+ kernel/cpu.c        | 15 +++++++++++++++
+ kernel/sched/core.c |  4 ++++
+ 3 files changed, 24 insertions(+)
+
+diff --git a/include/linux/cpu.h b/include/linux/cpu.h
+index aab4273810e3..e67645924404 100644
+--- a/include/linux/cpu.h
++++ b/include/linux/cpu.h
+@@ -118,6 +118,8 @@ extern void cpu_hotplug_disable(void);
+ extern void cpu_hotplug_enable(void);
+ void clear_tasks_mm_cpumask(int cpu);
+ int cpu_down(unsigned int cpu);
++extern void pin_current_cpu(void);
++extern void unpin_current_cpu(void);
+ 
+ #else /* CONFIG_HOTPLUG_CPU */
+ 
+@@ -129,6 +131,9 @@ static inline int  cpus_read_trylock(void) { return true; }
+ static inline void lockdep_assert_cpus_held(void) { }
+ static inline void cpu_hotplug_disable(void) { }
+ static inline void cpu_hotplug_enable(void) { }
++static inline void pin_current_cpu(void) { }
++static inline void unpin_current_cpu(void) { }
++
+ #endif	/* !CONFIG_HOTPLUG_CPU */
+ 
+ /* Wrappers which go away once all code is converted */
+diff --git a/kernel/cpu.c b/kernel/cpu.c
+index d6fd362afc81..89a96cc14b39 100644
+--- a/kernel/cpu.c
++++ b/kernel/cpu.c
+@@ -283,6 +283,21 @@ static int cpu_hotplug_disabled;
+ 
+ #ifdef CONFIG_HOTPLUG_CPU
+ 
++/**
++ * pin_current_cpu - Prevent the current cpu from being unplugged
++ */
++void pin_current_cpu(void)
++{
++
++}
++
++/**
++ * unpin_current_cpu - Allow unplug of current cpu
++ */
++void unpin_current_cpu(void)
++{
++}
++
+ DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
+ 
+ void cpus_read_lock(void)
+diff --git a/kernel/sched/core.c b/kernel/sched/core.c
+index ba6f445ac9e8..ed79f921a84e 100644
+--- a/kernel/sched/core.c
++++ b/kernel/sched/core.c
+@@ -7243,6 +7243,7 @@ void migrate_disable(void)
+ 	}
+ 
+ 	preempt_disable();
++	pin_current_cpu();
+ 
+ 	migrate_disable_update_cpus_allowed(p);
+ 	p->migrate_disable = 1;
+@@ -7308,12 +7309,15 @@ void migrate_enable(void)
+ 			arg.task = p;
+ 			arg.dest_cpu = dest_cpu;
+ 
++			unpin_current_cpu();
+ 			preempt_enable();
+ 			stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
+ 			tlb_migrate_finish(p->mm);
++
+ 			return;
+ 		}
+ 	}
++	unpin_current_cpu();
+ 	preempt_enable();
+ }
+ EXPORT_SYMBOL(migrate_enable);
+-- 
+2.36.1
+