Commit-ID: 29d5e0476e1c4a513859e7858845ad172f560389 Gitweb: http://git.kernel.org/tip/29d5e0476e1c4a513859e7858845ad172f560389 Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Fri, 20 Apr 2012 13:05:45 +0000 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Cc: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> Cc: Matt Turner <mattst88@xxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxxx> Cc: Mike Frysinger <vapier@xxxxxxxxxx> Cc: Jesper Nilsson <jesper.nilsson@xxxxxxxx> Cc: Richard Kuo <rkuo@xxxxxxxxxxxxxx> Cc: Tony Luck <tony.luck@xxxxxxxxx> Cc: Hirokazu Takata <takata@xxxxxxxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: David Howells <dhowells@xxxxxxxxxx> Cc: James E.J. Bottomley <jejb@xxxxxxxxxxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> Cc: Paul Mundt <lethal@xxxxxxxxxxxx> Cc: David S. Miller <davem@xxxxxxxxxxxxx> Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx> Cc: Richard Weinberger <richard@xxxxxx> Cc: x86@xxxxxxxxxx Acked-by: Venkatesh Pallipadi <venki@xxxxxxxxxx> Link: http://lkml.kernel.org/r/20120420124557.102478630@xxxxxxxxxxxxx --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html