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: 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 --- arch/Kconfig | 3 + kernel/cpu.c | 2 - kernel/sched/core.c | 2 + kernel/smpboot.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++ kernel/smpboot.h | 10 ++++++ 5 files changed, 99 insertions(+), 1 deletion(-) Index: linux-2.6/arch/Kconfig =================================================================== --- linux-2.6.orig/arch/Kconfig +++ linux-2.6/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 Index: linux-2.6/kernel/cpu.c =================================================================== --- linux-2.6.orig/kernel/cpu.c +++ linux-2.6/kernel/cpu.c @@ -316,7 +316,7 @@ static int __cpuinit _cpu_up(unsigned in } /* 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)); Index: linux-2.6/kernel/sched/core.c =================================================================== --- linux-2.6.orig/kernel/sched/core.c +++ linux-2.6/kernel/sched/core.c @@ -83,6 +83,7 @@ #include "sched.h" #include "../workqueue_sched.h" +#include "../smpboot.h" #define CREATE_TRACE_POINTS #include @@ -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(); Index: linux-2.6/kernel/smpboot.c =================================================================== --- linux-2.6.orig/kernel/smpboot.c +++ linux-2.6/kernel/smpboot.c @@ -1,12 +1,95 @@ /* * Common SMP CPU bringup/teardown functions */ +#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 idle_thread_init(cpu); } Index: linux-2.6/kernel/smpboot.h =================================================================== --- linux-2.6.orig/kernel/smpboot.h +++ linux-2.6/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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/