/* * Generic helpers for smp ipi calls * * (C) Jens Axboe <jens.axboe@oracle.com> 2008 */ #include <linux/rcupdate.h> #include <linux/rculist.h> #include <linux/kernel.h> #include <linux/module.h> #include <linux/percpu.h> #include <linux/init.h> #include <linux/gfp.h> #include <linux/smp.h> #include <linux/cpu.h> #ifdef CONFIG_USE_GENERIC_SMP_HELPERS static struct { struct list_head queue; raw_spinlock_t lock; } call_function __cacheline_aligned_in_smp = { .queue = LIST_HEAD_INIT(call_function.queue), .lock = __RAW_SPIN_LOCK_UNLOCKED(call_function.lock), }; enum { CSD_FLAG_LOCK = 0x01, }; struct call_function_data { struct call_single_data csd; atomic_t refs; cpumask_var_t cpumask; }; static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data); struct call_single_queue { struct list_head list; raw_spinlock_t lock; }; static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_queue, call_single_queue); static int hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu) { long cpu = (long)hcpu; struct call_function_data *cfd = &per_cpu(cfd_data, cpu); switch (action) { case CPU_UP_PREPARE: case CPU_UP_PREPARE_FROZEN: if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL, cpu_to_node(cpu))) return notifier_from_errno(-ENOMEM); break; #ifdef CONFIG_HOTPLUG_CPU case CPU_UP_CANCELED: case CPU_UP_CANCELED_FROZEN: case CPU_DEAD: case CPU_DEAD_FROZEN: free_cpumask_var(cfd->cpumask); break; #endif }; return NOTIFY_OK; } static struct notifier_block __cpuinitdata hotplug_cfd_notifier = { .notifier_call = hotplug_cfd, }; static int __cpuinit init_call_single_data(void) { void *cpu = (void *)(long)smp_processor_id(); int i; for_each_possible_cpu(i) { struct call_single_queue *q = &per_cpu(call_single_queue, i); raw_spin_lock_init(&q->lock); INIT_LIST_HEAD(&q->list); } hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu); register_cpu_notifier(&hotplug_cfd_notifier); return 0; } early_initcall(init_call_single_data); /* * csd_lock/csd_unlock used to serialize access to per-cpu csd resources * * For non-synchronous ipi calls the csd can still be in use by the * previous function call. For multi-cpu calls its even more interesting * as we'll have to ensure no other cpu is observing our csd. */ static void csd_lock_wait(struct call_single_data *data) { while (data->flags & CSD_FLAG_LOCK) cpu_relax(); } static void csd_lock(struct call_single_data *data) { csd_lock_wait(data); data->flags = CSD_FLAG_LOCK; /* * prevent CPU from reordering the above assignment * to ->flags with any subsequent assignments to other * fields of the specified call_single_data structure: */ smp_mb(); } static void csd_unlock(struct call_single_data *data) { WARN_ON(!(data->flags & CSD_FLAG_LOCK)); /* * ensure we're all done before releasing data: */ smp_mb(); data->flags &= ~CSD_FLAG_LOCK; } /* * Insert a previously allocated call_single_data element * for execution on the given CPU. data must already have * ->func, ->info, and ->flags set. */ static void generic_exec_single(int cpu, struct call_single_data *data, int wait) { struct call_single_queue *dst = &per_cpu(call_single_queue, cpu); unsigned long flags; int ipi; raw_spin_lock_irqsave(&dst->lock, flags); ipi = list_empty(&dst->list); list_add_tail(&data->list, &dst->list); raw_spin_unlock_irqrestore(&dst->lock, flags); /* * The list addition should be visible before sending the IPI * handler locks the list to pull the entry off it because of * normal cache coherency rules implied by spinlocks. * * If IPIs can go out of order to the cache coherency protocol * in an architecture, sufficient synchronisation should be added * to arch code to make it appear to obey cache coherency WRT * locking and barrier primitives. Generic code isn't really * equipped to do the right thing... */ if (ipi) arch_send_call_function_single_ipi(cpu); if (wait) csd_lock_wait(data); } /* * Invoked by arch to handle an IPI for call function. Must be called with * interrupts disabled. */ void generic_smp_call_function_interrupt(void) { struct call_function_data *data; int cpu = smp_processor_id(); /* * Shouldn't receive this interrupt on a cpu that is not yet online. */ WARN_ON_ONCE(!cpu_online(cpu)); /* * Ensure entry is visible on call_function_queue after we have * entered the IPI. See comment in smp_call_function_many. * If we don't have this, then we may miss an entry on the list * and never get another IPI to process it. */ smp_mb(); /* * It's ok to use list_for_each_rcu() here even though we may * delete 'pos', since list_del_rcu() doesn't clear ->next */ list_for_each_entry_rcu(data, &call_function.queue, csd.list) { int refs; smp_call_func_t func; /* * Since we walk the list without any locks, we might * see an entry that was completed, removed from the * list and is in the process of being reused. * * We must check that the cpu is in the cpumask before * checking the refs, and both must be set before * executing the callback on this cpu. */ if (!cpumask_test_cpu(cpu, data->cpumask)) continue; smp_rmb(); if (atomic_read(&data->refs) == 0) continue; func = data->csd.func; /* save for later warn */ func(data->csd.info); /* * If the cpu mask is not still set then func enabled * interrupts (BUG), and this cpu took another smp call * function interrupt and executed func(info) twice * on this cpu. That nested execution decremented refs. */ if (!cpumask_test_and_clear_cpu(cpu, data->cpumask)) { WARN(1, "%pf enabled interrupts and double executed\n", func); continue; } refs = atomic_dec_return(&data->refs); WARN_ON(refs < 0); if (refs) continue; WARN_ON(!cpumask_empty(data->cpumask)); raw_spin_lock(&call_function.lock); list_del_rcu(&data->csd.list); raw_spin_unlock(&call_function.lock); csd_unlock(&data->csd); } } /* * Invoked by arch to handle an IPI for call function single. Must be * called from the arch with interrupts disabled. */ void generic_smp_call_function_single_interrupt(void) { struct call_single_queue *q = &__get_cpu_var(call_single_queue); unsigned int data_flags; LIST_HEAD(list); /* * Shouldn't receive this interrupt on a cpu that is not yet online. */ WARN_ON_ONCE(!cpu_online(smp_processor_id())); raw_spin_lock(&q->lock); list_replace_init(&q->list, &list); raw_spin_unlock(&q->lock); while (!list_empty(&list)) { struct call_single_data *data; data = list_entry(list.next, struct call_single_data, list); list_del(&data->list); /* * 'data' can be invalid after this call if flags == 0 * (when called through generic_exec_single()), * so save them away before making the call: */ data_flags = data->flags; data->func(data->info); /* * Unlocked CSDs are valid through generic_exec_single(): */ if (data_flags & CSD_FLAG_LOCK) csd_unlock(data); } } static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data); /* * smp_call_function_single - Run a function on a specific CPU * @func: The function to run. This must be fast and non-blocking. * @info: An arbitrary pointer to pass to the function. * @wait: If true, wait until function has completed on other CPUs. * * Returns 0 on success, else a negative status code. */ int smp_call_function_single(int cpu, smp_call_func_t func, void *info, int wait) { struct call_single_data d = { .flags = 0, }; unsigned long flags; int this_cpu; int err = 0; /* * prevent preemption and reschedule on another processor, * as well as CPU removal */ this_cpu = get_cpu(); /* * Can deadlock when called with interrupts disabled. * We allow cpu's that are not yet online though, as no one else can * send smp call function interrupt to this cpu and as such deadlocks * can't happen. */ WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled() && !oops_in_progress); if (cpu == this_cpu) { local_irq_save(flags); func(info); local_irq_restore(flags); } else { if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) { struct call_single_data *data = &d; if (!wait) data = &__get_cpu_var(csd_data); csd_lock(data); data->func = func; data->info = info; generic_exec_single(cpu, data, wait); } else { err = -ENXIO; /* CPU not online */ } } put_cpu(); return err; } EXPORT_SYMBOL(smp_call_function_single); /* * smp_call_function_any - Run a function on any of the given cpus * @mask: The mask of cpus it can run on. * @func: The function to run. This must be fast and non-blocking. * @info: An arbitrary pointer to pass to the function. * @wait: If true, wait until function has completed. * * Returns 0 on success, else a negative status code (if no cpus were online). * Note that @wait will be implicitly turned on in case of allocation failures, * since we fall back to on-stack allocation. * * Selection preference: * 1) current cpu if in @mask * 2) any cpu of current node if in @mask * 3) any other online cpu in @mask */ int smp_call_function_any(const struct cpumask *mask, smp_call_func_t func, void *info, int wait) { unsigned int cpu; const struct cpumask *nodemask; int ret; /* Try for same CPU (cheapest) */ cpu = get_cpu(); if (cpumask_test_cpu(cpu, mask)) goto call; /* Try for same node. */ nodemask = cpumask_of_node(cpu_to_node(cpu)); for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids; cpu = cpumask_next_and(cpu, nodemask, mask)) { if (cpu_online(cpu)) goto call; } /* Any online will do: smp_call_function_single handles nr_cpu_ids. */ cpu = cpumask_any_and(mask, cpu_online_mask); call: ret = smp_call_function_single(cpu, func, info, wait); put_cpu(); return ret; } EXPORT_SYMBOL_GPL(smp_call_function_any); /** * __smp_call_function_single(): Run a function on a specific CPU * @cpu: The CPU to run on. * @data: Pre-allocated and setup data structure * @wait: If true, wait until function has completed on specified CPU. * * Like smp_call_function_single(), but allow caller to pass in a * pre-allocated data structure. Useful for embedding @data inside * other structures, for instance. */ void __smp_call_function_single(int cpu, struct call_single_data *data, int wait) { unsigned int this_cpu; unsigned long flags; this_cpu = get_cpu(); /* * Can deadlock when called with interrupts disabled. * We allow cpu's that are not yet online though, as no one else can * send smp call function interrupt to this cpu and as such deadlocks * can't happen. */ WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled() && !oops_in_progress); if (cpu == this_cpu) { local_irq_save(flags); data->func(data->info); local_irq_restore(flags); } else { csd_lock(data); generic_exec_single(cpu, data, wait); } put_cpu(); } /** * smp_call_function_many(): Run a function on a set of other CPUs. * @mask: The set of cpus to run on (only runs on online subset). * @func: The function to run. This must be fast and non-blocking. * @info: An arbitrary pointer to pass to the function. * @wait: If true, wait (atomically) until function has completed * on other CPUs. * * If @wait is true, then returns once @func has returned. * * You must not call this function with disabled interrupts or from a * hardware interrupt handler or from a bottom half handler. Preemption * must be disabled when calling this function. */ void smp_call_function_many(const struct cpumask *mask, smp_call_func_t func, void *info, bool wait) { struct call_function_data *data; unsigned long flags; int refs, cpu, next_cpu, this_cpu = smp_processor_id(); /* * Can deadlock when called with interrupts disabled. * We allow cpu's that are not yet online though, as no one else can * send smp call function interrupt to this cpu and as such deadlocks * can't happen. */ WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled() && !oops_in_progress && !early_boot_irqs_disabled); /* Try to fastpath. So, what's a CPU they want? Ignoring this one. */ cpu = cpumask_first_and(mask, cpu_online_mask); if (cpu == this_cpu) cpu = cpumask_next_and(cpu, mask, cpu_online_mask); /* No online cpus? We're done. */ if (cpu >= nr_cpu_ids) return; /* Do we have another CPU which isn't us? */ next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask); if (next_cpu == this_cpu) next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask); /* Fastpath: do that cpu by itself. */ if (next_cpu >= nr_cpu_ids) { smp_call_function_single(cpu, func, info, wait); return; } data = &__get_cpu_var(cfd_data); csd_lock(&data->csd); /* This BUG_ON verifies our reuse assertions and can be removed */ BUG_ON(atomic_read(&data->refs) || !cpumask_empty(data->cpumask)); /* * The global call function queue list add and delete are protected * by a lock, but the list is traversed without any lock, relying * on the rcu list add and delete to allow safe concurrent traversal. * We reuse the call function data without waiting for any grace * period after some other cpu removes it from the global queue. * This means a cpu might find our data block as it is being * filled out. * * We hold off the interrupt handler on the other cpu by * ordering our writes to the cpu mask vs our setting of the * refs counter. We assert only the cpu owning the data block * will set a bit in cpumask, and each bit will only be cleared * by the subject cpu. Each cpu must first find its bit is * set and then check that refs is set indicating the element is * ready to be processed, otherwise it must skip the entry. * * On the previous iteration refs was set to 0 by another cpu. * To avoid the use of transitivity, set the counter to 0 here * so the wmb will pair with the rmb in the interrupt handler. */ atomic_set(&data->refs, 0); /* convert 3rd to 1st party write */ data->csd.func = func; data->csd.info = info; /* Ensure 0 refs is visible before mask. Also orders func and info */ smp_wmb(); /* We rely on the "and" being processed before the store */ cpumask_and(data->cpumask, mask, cpu_online_mask); cpumask_clear_cpu(this_cpu, data->cpumask); refs = cpumask_weight(data->cpumask); /* Some callers race with other cpus changing the passed mask */ if (unlikely(!refs)) { csd_unlock(&data->csd); return; } raw_spin_lock_irqsave(&call_function.lock, flags); /* * Place entry at the _HEAD_ of the list, so that any cpu still * observing the entry in generic_smp_call_function_interrupt() * will not miss any other list entries: */ list_add_rcu(&data->csd.list, &call_function.queue); /* * We rely on the wmb() in list_add_rcu to complete our writes * to the cpumask before this write to refs, which indicates * data is on the list and is ready to be processed. */ atomic_set(&data->refs, refs); raw_spin_unlock_irqrestore(&call_function.lock, flags); /* * Make the list addition visible before sending the ipi. * (IPIs must obey or appear to obey normal Linux cache * coherency rules -- see comment in generic_exec_single). */ smp_mb(); /* Send a message to all CPUs in the map */ arch_send_call_function_ipi_mask(data->cpumask); /* Optionally wait for the CPUs to complete */ if (wait) csd_lock_wait(&data->csd); } EXPORT_SYMBOL(smp_call_function_many); /** * smp_call_function(): Run a function on all other CPUs. * @func: The function to run. This must be fast and non-blocking. * @info: An arbitrary pointer to pass to the function. * @wait: If true, wait (atomically) until function has completed * on other CPUs. * * Returns 0. * * If @wait is true, then returns once @func has returned; otherwise * it returns just before the target cpu calls @func. * * You must not call this function with disabled interrupts or from a * hardware interrupt handler or from a bottom half handler. */ int smp_call_function(smp_call_func_t func, void *info, int wait) { preempt_disable(); smp_call_function_many(cpu_online_mask, func, info, wait); preempt_enable(); return 0; } EXPORT_SYMBOL(smp_call_function); void ipi_call_lock(void) { raw_spin_lock(&call_function.lock); } void ipi_call_unlock(void) { raw_spin_unlock(&call_function.lock); } void ipi_call_lock_irq(void) { raw_spin_lock_irq(&call_function.lock); } void ipi_call_unlock_irq(void) { raw_spin_unlock_irq(&call_function.lock); } #endif /* USE_GENERIC_SMP_HELPERS */ /* Setup configured maximum number of CPUs to activate */ unsigned int setup_max_cpus = NR_CPUS; EXPORT_SYMBOL(setup_max_cpus); /* * Setup routine for controlling SMP activation * * Command-line option of "nosmp" or "maxcpus=0" will disable SMP * activation entirely (the MPS table probe still happens, though). * * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer * greater than 0, limits the maximum number of CPUs activated in * SMP mode to <NUM>. */ void __weak arch_disable_smp_support(void) { } static int __init nosmp(char *str) { setup_max_cpus = 0; arch_disable_smp_support(); return 0; } early_param("nosmp", nosmp); /* this is hard limit */ static int __init nrcpus(char *str) { int nr_cpus; get_option(&str, &nr_cpus); if (nr_cpus > 0 && nr_cpus < nr_cpu_ids) nr_cpu_ids = nr_cpus; return 0; } early_param("nr_cpus", nrcpus); static int __init maxcpus(char *str) { get_option(&str, &setup_max_cpus); if (setup_max_cpus == 0) arch_disable_smp_support(); return 0; } early_param("maxcpus", maxcpus); /* Setup number of possible processor ids */ int nr_cpu_ids __read_mostly = NR_CPUS; EXPORT_SYMBOL(nr_cpu_ids); /* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */ void __init setup_nr_cpu_ids(void) { nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1; } /* Called by boot processor to activate the rest. */ void __init smp_init(void) { unsigned int cpu; /* FIXME: This should be done in userspace --RR */ for_each_present_cpu(cpu) { if (num_online_cpus() >= setup_max_cpus) break; if (!cpu_online(cpu)) cpu_up(cpu); } /* Any cleanup work */ printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus()); smp_cpus_done(setup_max_cpus); } /* * Call a function on all processors. May be used during early boot while * early_boot_irqs_disabled is set. Use local_irq_save/restore() instead * of local_irq_disable/enable(). */ int on_each_cpu(void (*func) (void *info), void *info, int wait) { unsigned long flags; int ret = 0; preempt_disable(); ret = smp_call_function(func, info, wait); local_irq_save(flags); func(info); local_irq_restore(flags); preempt_enable(); return ret; } EXPORT_SYMBOL(on_each_cpu);