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Commit 29d5e047 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Howells <dhowells@redhat.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: x86@kernel.org
Acked-by: default avatarVenkatesh Pallipadi <venki@google.com>
Link: http://lkml.kernel.org/r/20120420124557.102478630@linutronix.de
parent 38498a67

arch/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -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

kernel/cpu.c

+1 −1
Original line number Diff line number Diff line
@@ -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));

kernel/sched/core.c

+2 −0
Original line number Diff line number Diff line
@@ -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();

kernel/smpboot.c

+83 −1
Original line number Diff line number Diff line 
/*

 * 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);

}

kernel/smpboot.h

+10 −0
Original line number Diff line number Diff line 
#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