From: Heiko Carstens Introduce stop_machine_create/destroy. With this interface subsystems that need a non-failing stop_machine environment can create the stop_machine machine threads before actually calling stop_machine. When the threads aren't needed anymore they can be killed with stop_machine_destroy again. When stop_machine gets called and the threads aren't present they will be created and destroyed automatically. This restores the old behaviour of stop_machine. This patch also converts cpu hotplug to the new interface since it is special: cpu_down calls __stop_machine instead of stop_machine. However the kstop threads will only be created when stop_machine gets called. Changing the code so that the threads would be created automatically on __stop_machine is currently not possible: when __stop_machine gets called we hold cpu_add_remove_lock, which is the same lock that create_rt_workqueue would take. So the workqueue needs to be created before the cpu hotplug code locks cpu_add_remove_lock. Signed-off-by: Heiko Carstens --- include/linux/stop_machine.h | 22 +++++++++++++++++ kernel/cpu.c | 6 +++- kernel/stop_machine.c | 55 +++++++++++++++++++++++++++++++++++-------- 3 files changed, 72 insertions(+), 11 deletions(-) Index: linux-2.6/kernel/stop_machine.c =================================================================== --- linux-2.6.orig/kernel/stop_machine.c +++ linux-2.6/kernel/stop_machine.c @@ -38,7 +38,10 @@ struct stop_machine_data { static unsigned int num_threads; static atomic_t thread_ack; static DEFINE_MUTEX(lock); - +/* setup_lock protects refcount, stop_machine_wq and stop_machine_work. */ +static DEFINE_MUTEX(setup_lock); +/* Users of stop_machine. */ +static int refcount; static struct workqueue_struct *stop_machine_wq; static struct stop_machine_data active, idle; static const cpumask_t *active_cpus; @@ -109,6 +112,43 @@ static int chill(void *unused) return 0; } +int stop_machine_create(void) +{ + mutex_lock(&setup_lock); + if (refcount) + goto done; + stop_machine_wq = create_rt_workqueue("kstop"); + if (!stop_machine_wq) + goto err_out; + stop_machine_work = alloc_percpu(struct work_struct); + if (!stop_machine_work) + goto err_out; +done: + refcount++; + mutex_unlock(&setup_lock); + return 0; + +err_out: + if (stop_machine_wq) + destroy_workqueue(stop_machine_wq); + mutex_unlock(&setup_lock); + return -ENOMEM; +} +EXPORT_SYMBOL_GPL(stop_machine_create); + +void stop_machine_destroy(void) +{ + mutex_lock(&setup_lock); + refcount--; + if (refcount) + goto done; + destroy_workqueue(stop_machine_wq); + free_percpu(stop_machine_work); +done: + mutex_unlock(&setup_lock); +} +EXPORT_SYMBOL_GPL(stop_machine_destroy); + int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus) { struct work_struct *sm_work; @@ -146,19 +186,14 @@ int stop_machine(int (*fn)(void *), void { int ret; + ret = stop_machine_create(); + if (ret) + return ret; /* No CPUs can come up or down during this. */ get_online_cpus(); ret = __stop_machine(fn, data, cpus); put_online_cpus(); - + stop_machine_destroy(); return ret; } EXPORT_SYMBOL_GPL(stop_machine); - -static int __init stop_machine_init(void) -{ - stop_machine_wq = create_rt_workqueue("kstop"); - stop_machine_work = alloc_percpu(struct work_struct); - return 0; -} -core_initcall(stop_machine_init); Index: linux-2.6/kernel/cpu.c =================================================================== --- linux-2.6.orig/kernel/cpu.c +++ linux-2.6/kernel/cpu.c @@ -290,8 +290,11 @@ out_release: int __ref cpu_down(unsigned int cpu) { - int err = 0; + int err; + err = stop_machine_create(); + if (err) + return err; cpu_maps_update_begin(); if (cpu_hotplug_disabled) { @@ -318,6 +321,7 @@ int __ref cpu_down(unsigned int cpu) out: cpu_maps_update_done(); + stop_machine_destroy(); return err; } EXPORT_SYMBOL(cpu_down); Index: linux-2.6/include/linux/stop_machine.h =================================================================== --- linux-2.6.orig/include/linux/stop_machine.h +++ linux-2.6/include/linux/stop_machine.h @@ -35,6 +35,24 @@ int stop_machine(int (*fn)(void *), void * won't come or go while it's being called. Used by hotplug cpu. */ int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus); + +/** + * stop_machine_create: create all stop_machine threads + * + * Description: This causes all stop_machine threads to be created before + * stop_machine actually gets called. This can be used by subsystems that + * need a non failing stop_machine infrastructure. + */ +int stop_machine_create(void); + +/** + * stop_machine_destroy: destroy all stop_machine threads + * + * Description: This causes all stop_machine threads which were created with + * stop_machine_create to be destroyed again. + */ +void stop_machine_destroy(void); + #else static inline int stop_machine(int (*fn)(void *), void *data, @@ -46,5 +64,9 @@ static inline int stop_machine(int (*fn) local_irq_enable(); return ret; } + +static inline int stop_machine_create(void) { return 0; } +static inline void stop_machine_destroy(void) { } + #endif /* CONFIG_SMP */ #endif /* _LINUX_STOP_MACHINE */ -- -- 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/