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

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
......@@ -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
......
......@@ -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));
......
......@@ -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();
......
/*
* 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);
}
#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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