From 1142d810298e694754498dbb4983fcb6cb7fd884 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 6 May 2010 18:49:20 +0200 Subject: cpu_stop: implement stop_cpu[s]() Implement a simplistic per-cpu maximum priority cpu monopolization mechanism. A non-sleeping callback can be scheduled to run on one or multiple cpus with maximum priority monopolozing those cpus. This is primarily to replace and unify RT workqueue usage in stop_machine and scheduler migration_thread which currently is serving multiple purposes. Four functions are provided - stop_one_cpu(), stop_one_cpu_nowait(), stop_cpus() and try_stop_cpus(). This is to allow clean sharing of resources among stop_cpu and all the migration thread users. One stopper thread per cpu is created which is currently named "stopper/CPU". This will eventually replace the migration thread and take on its name. * This facility was originally named cpuhog and lived in separate files but Peter Zijlstra nacked the name and thus got renamed to cpu_stop and moved into stop_machine.c. * Better reporting of preemption leak as per Peter's suggestion. Signed-off-by: Tejun Heo Acked-by: Peter Zijlstra Cc: Oleg Nesterov Cc: Dimitri Sivanich --- include/linux/stop_machine.h | 39 +++++++++++++++++++++++++++++++++++---- 1 file changed, 35 insertions(+), 4 deletions(-) (limited to 'include/linux/stop_machine.h') diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h index baba3a23a814..efcbd6c37947 100644 --- a/include/linux/stop_machine.h +++ b/include/linux/stop_machine.h @@ -1,15 +1,46 @@ #ifndef _LINUX_STOP_MACHINE #define _LINUX_STOP_MACHINE -/* "Bogolock": stop the entire machine, disable interrupts. This is a - very heavy lock, which is equivalent to grabbing every spinlock - (and more). So the "read" side to such a lock is anything which - disables preeempt. */ + #include #include +#include #include #if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP) +/* + * stop_cpu[s]() is simplistic per-cpu maximum priority cpu + * monopolization mechanism. The caller can specify a non-sleeping + * function to be executed on a single or multiple cpus preempting all + * other processes and monopolizing those cpus until it finishes. + * + * Resources for this mechanism are preallocated when a cpu is brought + * up and requests are guaranteed to be served as long as the target + * cpus are online. + */ + +typedef int (*cpu_stop_fn_t)(void *arg); + +struct cpu_stop_work { + struct list_head list; /* cpu_stopper->works */ + cpu_stop_fn_t fn; + void *arg; + struct cpu_stop_done *done; +}; + +int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg); +void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, + struct cpu_stop_work *work_buf); +int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg); +int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg); + +/* + * stop_machine "Bogolock": stop the entire machine, disable + * interrupts. This is a very heavy lock, which is equivalent to + * grabbing every spinlock (and more). So the "read" side to such a + * lock is anything which disables preeempt. + */ + /** * stop_machine: freeze the machine on all CPUs and run this function * @fn: the function to run -- cgit v1.2.3 From 3fc1f1e27a5b807791d72e5d992aa33b668a6626 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 6 May 2010 18:49:20 +0200 Subject: stop_machine: reimplement using cpu_stop Reimplement stop_machine using cpu_stop. As cpu stoppers are guaranteed to be available for all online cpus, stop_machine_create/destroy() are no longer necessary and removed. With resource management and synchronization handled by cpu_stop, the new implementation is much simpler. Asking the cpu_stop to execute the stop_cpu() state machine on all online cpus with cpu hotplug disabled is enough. stop_machine itself doesn't need to manage any global resources anymore, so all per-instance information is rolled into struct stop_machine_data and the mutex and all static data variables are removed. The previous implementation created and destroyed RT workqueues as necessary which made stop_machine() calls highly expensive on very large machines. According to Dimitri Sivanich, preventing the dynamic creation/destruction makes booting faster more than twice on very large machines. cpu_stop resources are preallocated for all online cpus and should have the same effect. Signed-off-by: Tejun Heo Acked-by: Rusty Russell Acked-by: Peter Zijlstra Cc: Oleg Nesterov Cc: Dimitri Sivanich --- arch/s390/kernel/time.c | 1 - drivers/xen/manage.c | 14 +--- include/linux/stop_machine.h | 20 ------ kernel/cpu.c | 8 --- kernel/module.c | 14 +--- kernel/stop_machine.c | 158 +++++++++++-------------------------------- 6 files changed, 42 insertions(+), 173 deletions(-) (limited to 'include/linux/stop_machine.h') diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c index fba6dec156bf..03d96569f187 100644 --- a/arch/s390/kernel/time.c +++ b/arch/s390/kernel/time.c @@ -390,7 +390,6 @@ static void __init time_init_wq(void) if (time_sync_wq) return; time_sync_wq = create_singlethread_workqueue("timesync"); - stop_machine_create(); } /* diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c index 2ac4440e7b08..8943b8ccee1a 100644 --- a/drivers/xen/manage.c +++ b/drivers/xen/manage.c @@ -80,12 +80,6 @@ static void do_suspend(void) shutting_down = SHUTDOWN_SUSPEND; - err = stop_machine_create(); - if (err) { - printk(KERN_ERR "xen suspend: failed to setup stop_machine %d\n", err); - goto out; - } - #ifdef CONFIG_PREEMPT /* If the kernel is preemptible, we need to freeze all the processes to prevent them from being in the middle of a pagetable update @@ -93,7 +87,7 @@ static void do_suspend(void) err = freeze_processes(); if (err) { printk(KERN_ERR "xen suspend: freeze failed %d\n", err); - goto out_destroy_sm; + goto out; } #endif @@ -136,12 +130,8 @@ out_resume: out_thaw: #ifdef CONFIG_PREEMPT thaw_processes(); - -out_destroy_sm: -#endif - stop_machine_destroy(); - out: +#endif shutting_down = SHUTDOWN_INVALID; } #endif /* CONFIG_PM_SLEEP */ diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h index efcbd6c37947..0e552e72a4c4 100644 --- a/include/linux/stop_machine.h +++ b/include/linux/stop_machine.h @@ -67,23 +67,6 @@ int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus); */ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *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, @@ -96,8 +79,5 @@ static inline int stop_machine(int (*fn)(void *), void *data, 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 */ diff --git a/kernel/cpu.c b/kernel/cpu.c index 914aedcde849..545777574779 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -266,9 +266,6 @@ int __ref cpu_down(unsigned int cpu) { int err; - err = stop_machine_create(); - if (err) - return err; cpu_maps_update_begin(); if (cpu_hotplug_disabled) { @@ -280,7 +277,6 @@ int __ref cpu_down(unsigned int cpu) out: cpu_maps_update_done(); - stop_machine_destroy(); return err; } EXPORT_SYMBOL(cpu_down); @@ -361,9 +357,6 @@ int disable_nonboot_cpus(void) { int cpu, first_cpu, error; - error = stop_machine_create(); - if (error) - return error; cpu_maps_update_begin(); first_cpu = cpumask_first(cpu_online_mask); /* @@ -394,7 +387,6 @@ int disable_nonboot_cpus(void) printk(KERN_ERR "Non-boot CPUs are not disabled\n"); } cpu_maps_update_done(); - stop_machine_destroy(); return error; } diff --git a/kernel/module.c b/kernel/module.c index 1016b75b026a..0838246d8c94 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -723,16 +723,8 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user, return -EFAULT; name[MODULE_NAME_LEN-1] = '\0'; - /* Create stop_machine threads since free_module relies on - * a non-failing stop_machine call. */ - ret = stop_machine_create(); - if (ret) - return ret; - - if (mutex_lock_interruptible(&module_mutex) != 0) { - ret = -EINTR; - goto out_stop; - } + if (mutex_lock_interruptible(&module_mutex) != 0) + return -EINTR; mod = find_module(name); if (!mod) { @@ -792,8 +784,6 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user, out: mutex_unlock(&module_mutex); -out_stop: - stop_machine_destroy(); return ret; } diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 7e3f9182aef3..884c7a1afeed 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -388,174 +388,92 @@ enum stopmachine_state { /* Exit */ STOPMACHINE_EXIT, }; -static enum stopmachine_state state; struct stop_machine_data { - int (*fn)(void *); - void *data; - int fnret; + int (*fn)(void *); + void *data; + /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */ + unsigned int num_threads; + const struct cpumask *active_cpus; + + enum stopmachine_state state; + atomic_t thread_ack; }; -/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */ -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 struct cpumask *active_cpus; -static void __percpu *stop_machine_work; - -static void set_state(enum stopmachine_state newstate) +static void set_state(struct stop_machine_data *smdata, + enum stopmachine_state newstate) { /* Reset ack counter. */ - atomic_set(&thread_ack, num_threads); + atomic_set(&smdata->thread_ack, smdata->num_threads); smp_wmb(); - state = newstate; + smdata->state = newstate; } /* Last one to ack a state moves to the next state. */ -static void ack_state(void) +static void ack_state(struct stop_machine_data *smdata) { - if (atomic_dec_and_test(&thread_ack)) - set_state(state + 1); + if (atomic_dec_and_test(&smdata->thread_ack)) + set_state(smdata, smdata->state + 1); } -/* This is the actual function which stops the CPU. It runs - * in the context of a dedicated stopmachine workqueue. */ -static void stop_cpu(struct work_struct *unused) +/* This is the cpu_stop function which stops the CPU. */ +static int stop_machine_cpu_stop(void *data) { + struct stop_machine_data *smdata = data; enum stopmachine_state curstate = STOPMACHINE_NONE; - struct stop_machine_data *smdata = &idle; - int cpu = smp_processor_id(); - int err; + int cpu = smp_processor_id(), err = 0; + bool is_active; + + if (!smdata->active_cpus) + is_active = cpu == cpumask_first(cpu_online_mask); + else + is_active = cpumask_test_cpu(cpu, smdata->active_cpus); - if (!active_cpus) { - if (cpu == cpumask_first(cpu_online_mask)) - smdata = &active; - } else { - if (cpumask_test_cpu(cpu, active_cpus)) - smdata = &active; - } /* Simple state machine */ do { /* Chill out and ensure we re-read stopmachine_state. */ cpu_relax(); - if (state != curstate) { - curstate = state; + if (smdata->state != curstate) { + curstate = smdata->state; switch (curstate) { case STOPMACHINE_DISABLE_IRQ: local_irq_disable(); hard_irq_disable(); break; case STOPMACHINE_RUN: - /* On multiple CPUs only a single error code - * is needed to tell that something failed. */ - err = smdata->fn(smdata->data); - if (err) - smdata->fnret = err; + if (is_active) + err = smdata->fn(smdata->data); break; default: break; } - ack_state(); + ack_state(smdata); } } while (curstate != STOPMACHINE_EXIT); local_irq_enable(); + return err; } -/* Callback for CPUs which aren't supposed to do anything. */ -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 struct cpumask *cpus) { - struct work_struct *sm_work; - int i, ret; - - /* Set up initial state. */ - mutex_lock(&lock); - num_threads = num_online_cpus(); - active_cpus = cpus; - active.fn = fn; - active.data = data; - active.fnret = 0; - idle.fn = chill; - idle.data = NULL; - - set_state(STOPMACHINE_PREPARE); - - /* Schedule the stop_cpu work on all cpus: hold this CPU so one - * doesn't hit this CPU until we're ready. */ - get_cpu(); - for_each_online_cpu(i) { - sm_work = per_cpu_ptr(stop_machine_work, i); - INIT_WORK(sm_work, stop_cpu); - queue_work_on(i, stop_machine_wq, sm_work); - } - /* This will release the thread on our CPU. */ - put_cpu(); - flush_workqueue(stop_machine_wq); - ret = active.fnret; - mutex_unlock(&lock); - return ret; + struct stop_machine_data smdata = { .fn = fn, .data = data, + .num_threads = num_online_cpus(), + .active_cpus = cpus }; + + /* Set the initial state and stop all online cpus. */ + set_state(&smdata, STOPMACHINE_PREPARE); + return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata); } int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) { 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); -- cgit v1.2.3 From bbf1bb3eee86f2eef2baa14e600be454d09109ee Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sat, 8 May 2010 16:20:53 +0200 Subject: cpu_stop: add dummy implementation for UP When !CONFIG_SMP, cpu_stop functions weren't defined at all which could lead to build failures if UP code uses cpu_stop facility. Add dummy cpu_stop implementation for UP. The waiting variants execute the work function directly with preempt disabled and stop_one_cpu_nowait() schedules a workqueue work. Makefile and ifdefs around stop_machine implementation are updated to accomodate CONFIG_SMP && !CONFIG_STOP_MACHINE case. Signed-off-by: Tejun Heo Reported-by: Ingo Molnar --- include/linux/stop_machine.h | 69 ++++++++++++++++++++++++++++++++++++++++---- kernel/Makefile | 2 +- kernel/stop_machine.c | 4 +++ 3 files changed, 68 insertions(+), 7 deletions(-) (limited to 'include/linux/stop_machine.h') diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h index 0e552e72a4c4..6b524a0d02e4 100644 --- a/include/linux/stop_machine.h +++ b/include/linux/stop_machine.h @@ -6,8 +6,6 @@ #include #include -#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP) - /* * stop_cpu[s]() is simplistic per-cpu maximum priority cpu * monopolization mechanism. The caller can specify a non-sleeping @@ -18,9 +16,10 @@ * up and requests are guaranteed to be served as long as the target * cpus are online. */ - typedef int (*cpu_stop_fn_t)(void *arg); +#ifdef CONFIG_SMP + struct cpu_stop_work { struct list_head list; /* cpu_stopper->works */ cpu_stop_fn_t fn; @@ -34,12 +33,70 @@ void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg); int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg); +#else /* CONFIG_SMP */ + +#include + +struct cpu_stop_work { + struct work_struct work; + cpu_stop_fn_t fn; + void *arg; +}; + +static inline int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) +{ + int ret = -ENOENT; + preempt_disable(); + if (cpu == smp_processor_id()) + ret = fn(arg); + preempt_enable(); + return ret; +} + +static void stop_one_cpu_nowait_workfn(struct work_struct *work) +{ + struct cpu_stop_work *stwork = + container_of(work, struct cpu_stop_work, work); + preempt_disable(); + stwork->fn(stwork->arg); + preempt_enable(); +} + +static inline void stop_one_cpu_nowait(unsigned int cpu, + cpu_stop_fn_t fn, void *arg, + struct cpu_stop_work *work_buf) +{ + if (cpu == smp_processor_id()) { + INIT_WORK(&work_buf->work, stop_one_cpu_nowait_workfn); + work_buf->fn = fn; + work_buf->arg = arg; + schedule_work(&work_buf->work); + } +} + +static inline int stop_cpus(const struct cpumask *cpumask, + cpu_stop_fn_t fn, void *arg) +{ + if (cpumask_test_cpu(raw_smp_processor_id(), cpumask)) + return stop_one_cpu(raw_smp_processor_id(), fn, arg); + return -ENOENT; +} + +static inline int try_stop_cpus(const struct cpumask *cpumask, + cpu_stop_fn_t fn, void *arg) +{ + return stop_cpus(cpumask, fn, arg); +} + +#endif /* CONFIG_SMP */ + /* * stop_machine "Bogolock": stop the entire machine, disable * interrupts. This is a very heavy lock, which is equivalent to * grabbing every spinlock (and more). So the "read" side to such a * lock is anything which disables preeempt. */ +#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP) /** * stop_machine: freeze the machine on all CPUs and run this function @@ -67,7 +124,7 @@ int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus); */ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus); -#else +#else /* CONFIG_STOP_MACHINE && CONFIG_SMP */ static inline int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) @@ -79,5 +136,5 @@ static inline int stop_machine(int (*fn)(void *), void *data, return ret; } -#endif /* CONFIG_SMP */ -#endif /* _LINUX_STOP_MACHINE */ +#endif /* CONFIG_STOP_MACHINE && CONFIG_SMP */ +#endif /* _LINUX_STOP_MACHINE */ diff --git a/kernel/Makefile b/kernel/Makefile index a987aa1676b5..149e18ef1ab1 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -68,7 +68,7 @@ obj-$(CONFIG_USER_NS) += user_namespace.o obj-$(CONFIG_PID_NS) += pid_namespace.o obj-$(CONFIG_IKCONFIG) += configs.o obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o -obj-$(CONFIG_STOP_MACHINE) += stop_machine.o +obj-$(CONFIG_SMP) += stop_machine.o obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o obj-$(CONFIG_AUDIT) += audit.o auditfilter.o audit_watch.o obj-$(CONFIG_AUDITSYSCALL) += auditsc.o diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 5b20141a5ec1..ef51d1fcf5e6 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -375,6 +375,8 @@ static int __init cpu_stop_init(void) } early_initcall(cpu_stop_init); +#ifdef CONFIG_STOP_MACHINE + /* This controls the threads on each CPU. */ enum stopmachine_state { /* Dummy starting state for thread. */ @@ -477,3 +479,5 @@ int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) return ret; } EXPORT_SYMBOL_GPL(stop_machine); + +#endif /* CONFIG_STOP_MACHINE */ -- cgit v1.2.3