From 29d5e0476e1c4a513859e7858845ad172f560389 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 20 Apr 2012 13:05:45 +0000 Subject: 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 Cc: Peter Zijlstra Cc: Rusty Russell Cc: Paul E. McKenney Cc: Srivatsa S. Bhat Cc: Matt Turner Cc: Russell King Cc: Mike Frysinger Cc: Jesper Nilsson Cc: Richard Kuo Cc: Tony Luck Cc: Hirokazu Takata Cc: Ralf Baechle Cc: David Howells Cc: James E.J. Bottomley Cc: Benjamin Herrenschmidt Cc: Martin Schwidefsky Cc: Paul Mundt Cc: David S. Miller Cc: Chris Metcalf Cc: Richard Weinberger Cc: x86@kernel.org Acked-by: Venkatesh Pallipadi Link: http://lkml.kernel.org/r/20120420124557.102478630@linutronix.de --- kernel/smpboot.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 83 insertions(+), 1 deletion(-) (limited to 'kernel/smpboot.c') diff --git a/kernel/smpboot.c b/kernel/smpboot.c index 6dae6a3d2d59..ed1576981801 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -1,14 +1,96 @@ /* * Common SMP CPU bringup/teardown functions */ +#include +#include #include +#include +#include +#include #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); } -- cgit v1.2.1