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Date: Sat, 28 Apr 2012 02:05:03 -0700
From: tip-bot for Thomas Gleixner <tglx@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: mingo@...nel.org, jesper.nilsson@...s.com, rusty@...tcorp.com.au,
schwidefsky@...ibm.com, peterz@...radead.org, cmetcalf@...era.com,
tony.luck@...el.com, ralf@...ux-mips.org, linux@....linux.org.uk,
vapier@...too.org, tglx@...utronix.de, venki@...gle.com,
linux-kernel@...r.kernel.org, hpa@...or.com, richard@....at,
lethal@...ux-sh.org, srivatsa.bhat@...ux.vnet.ibm.com,
davem@...emloft.net, paulmck@...ux.vnet.ibm.com,
benh@...nel.crashing.org, dhowells@...hat.com, mattst88@...il.com,
jejb@...isc-linux.org, takata@...ux-m32r.org, rkuo@...eaurora.org
Subject: [tip:smp/hotplug] smp: Provide generic idle thread allocation
Commit-ID: 29d5e0476e1c4a513859e7858845ad172f560389
Gitweb: http://git.kernel.org/tip/29d5e0476e1c4a513859e7858845ad172f560389
Author: Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Fri, 20 Apr 2012 13:05:45 +0000
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 26 Apr 2012 12:06:09 +0200
smp: Provide generic idle thread allocation
All SMP architectures have magic to fork the idle task and to store it
for reusage when cpu hotplug is enabled. Provide a generic
infrastructure for it.
Create/reinit the idle thread for the cpu which is brought up in the
generic code and hand the thread pointer to the architecture code via
__cpu_up().
Note, that fork_idle() is called via a workqueue, because this
guarantees that the idle thread does not get a reference to a user
space VM. This can happen when the boot process did not bring up all
possible cpus and a later cpu_up() is initiated via the sysfs
interface. In that case fork_idle() would be called in the context of
the user space task and take a reference on the user space VM.
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rusty Russell <rusty@...tcorp.com.au>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
Cc: Matt Turner <mattst88@...il.com>
Cc: Russell King <linux@....linux.org.uk>
Cc: Mike Frysinger <vapier@...too.org>
Cc: Jesper Nilsson <jesper.nilsson@...s.com>
Cc: Richard Kuo <rkuo@...eaurora.org>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Hirokazu Takata <takata@...ux-m32r.org>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: David Howells <dhowells@...hat.com>
Cc: James E.J. Bottomley <jejb@...isc-linux.org>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Paul Mundt <lethal@...ux-sh.org>
Cc: David S. Miller <davem@...emloft.net>
Cc: Chris Metcalf <cmetcalf@...era.com>
Cc: Richard Weinberger <richard@....at>
Cc: x86@...nel.org
Acked-by: Venkatesh Pallipadi <venki@...gle.com>
Link: http://lkml.kernel.org/r/20120420124557.102478630@linutronix.de
---
arch/Kconfig | 3 ++
kernel/cpu.c | 2 +-
kernel/sched/core.c | 2 +
kernel/smpboot.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++-
kernel/smpboot.h | 10 ++++++
5 files changed, 99 insertions(+), 2 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 684eb5a..4f0d0f7 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -145,6 +145,9 @@ config HAVE_DMA_ATTRS
config USE_GENERIC_SMP_HELPERS
bool
+config GENERIC_SMP_IDLE_THREAD
+ bool
+
config HAVE_REGS_AND_STACK_ACCESS_API
bool
help
diff --git a/kernel/cpu.c b/kernel/cpu.c
index e58b99a..05c46ba 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -316,7 +316,7 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
}
/* Arch-specific enabling code. */
- ret = __cpu_up(cpu, NULL);
+ ret = __cpu_up(cpu, idle_thread_get(cpu));
if (ret != 0)
goto out_notify;
BUG_ON(!cpu_online(cpu));
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4603b9d..6a63cde 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -83,6 +83,7 @@
#include "sched.h"
#include "../workqueue_sched.h"
+#include "../smpboot.h"
#define CREATE_TRACE_POINTS
#include <trace/events/sched.h>
@@ -7049,6 +7050,7 @@ void __init sched_init(void)
/* May be allocated at isolcpus cmdline parse time */
if (cpu_isolated_map == NULL)
zalloc_cpumask_var(&cpu_isolated_map, GFP_NOWAIT);
+ idle_thread_set_boot_cpu();
#endif
init_sched_fair_class();
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 6dae6a3..ed15769 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -1,14 +1,96 @@
/*
* Common SMP CPU bringup/teardown functions
*/
+#include <linux/err.h>
+#include <linux/smp.h>
#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/percpu.h>
+#include <linux/workqueue.h>
#include "smpboot.h"
+#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
+struct create_idle {
+ struct work_struct work;
+ struct task_struct *idle;
+ struct completion done;
+ unsigned int cpu;
+};
+
+static void __cpuinit do_fork_idle(struct work_struct *work)
+{
+ struct create_idle *c = container_of(work, struct create_idle, work);
+
+ c->idle = fork_idle(c->cpu);
+ complete(&c->done);
+}
+
+static struct task_struct * __cpuinit idle_thread_create(unsigned int cpu)
+{
+ struct create_idle c_idle = {
+ .cpu = cpu,
+ .done = COMPLETION_INITIALIZER_ONSTACK(c_idle.done),
+ };
+
+ INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle);
+ schedule_work(&c_idle.work);
+ wait_for_completion(&c_idle.done);
+ destroy_work_on_stack(&c_idle.work);
+ return c_idle.idle;
+}
+
+/*
+ * For the hotplug case we keep the task structs around and reuse
+ * them.
+ */
+static DEFINE_PER_CPU(struct task_struct *, idle_threads);
+
+static inline struct task_struct *get_idle_for_cpu(unsigned int cpu)
+{
+ struct task_struct *tsk = per_cpu(idle_threads, cpu);
+
+ if (!tsk)
+ return idle_thread_create(cpu);
+ init_idle(tsk, cpu);
+ return tsk;
+}
+
+struct task_struct * __cpuinit idle_thread_get(unsigned int cpu)
+{
+ return per_cpu(idle_threads, cpu);
+}
+
+void __init idle_thread_set_boot_cpu(void)
+{
+ per_cpu(idle_threads, smp_processor_id()) = current;
+}
+
+/**
+ * idle_thread_init - Initialize the idle thread for a cpu
+ * @cpu: The cpu for which the idle thread should be initialized
+ *
+ * Creates the thread if it does not exist.
+ */
+static int __cpuinit idle_thread_init(unsigned int cpu)
+{
+ struct task_struct *idle = get_idle_for_cpu(cpu);
+
+ if (IS_ERR(idle)) {
+ printk(KERN_ERR "failed fork for CPU %u\n", cpu);
+ return PTR_ERR(idle);
+ }
+ per_cpu(idle_threads, cpu) = idle;
+ return 0;
+}
+#else
+static inline int idle_thread_init(unsigned int cpu) { return 0; }
+#endif
+
/**
* smpboot_prepare - generic smpboot preparation
*/
int __cpuinit smpboot_prepare(unsigned int cpu)
{
- return 0;
+ return idle_thread_init(cpu);
}
diff --git a/kernel/smpboot.h b/kernel/smpboot.h
index d88e771..7943bbb 100644
--- a/kernel/smpboot.h
+++ b/kernel/smpboot.h
@@ -1,6 +1,16 @@
#ifndef SMPBOOT_H
#define SMPBOOT_H
+struct task_struct;
+
int smpboot_prepare(unsigned int cpu);
+#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
+struct task_struct *idle_thread_get(unsigned int cpu);
+void idle_thread_set_boot_cpu(void);
+#else
+static inline struct task_struct *idle_thread_get(unsigned int cpu) { return NULL; }
+static inline void idle_thread_set_boot_cpu(void) { }
+#endif
+
#endif
--
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