Add generic helpers for arch IPI function calls
This adds kernel/smp.c which contains helpers for IPI function calls. In
addition to supporting the existing smp_call_function() in a more efficient
manner, it also adds a more scalable variant called smp_call_function_single()
for calling a given function on a single CPU only.
The core of this is based on the x86-64 patch from Nick Piggin, lots of
changes since then. "Alan D. Brunelle" <Alan.Brunelle@hp.com> has
contributed lots of fixes and suggestions as well. Also thanks to
Paul E. McKenney <paulmck@linux.vnet.ibm.com> for reviewing RCU usage
and getting rid of the data allocation fallback deadlock.
Acked-by: Ingo Molnar <mingo@elte.hu>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/kernel/smp.c b/kernel/smp.c
new file mode 100644
index 0000000..f77b75c
--- /dev/null
+++ b/kernel/smp.c
@@ -0,0 +1,383 @@
+/*
+ * Generic helpers for smp ipi calls
+ *
+ * (C) Jens Axboe <jens.axboe@oracle.com> 2008
+ *
+ */
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/rcupdate.h>
+#include <linux/smp.h>
+
+static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
+static LIST_HEAD(call_function_queue);
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock);
+
+enum {
+ CSD_FLAG_WAIT = 0x01,
+ CSD_FLAG_ALLOC = 0x02,
+};
+
+struct call_function_data {
+ struct call_single_data csd;
+ spinlock_t lock;
+ unsigned int refs;
+ cpumask_t cpumask;
+ struct rcu_head rcu_head;
+};
+
+struct call_single_queue {
+ struct list_head list;
+ spinlock_t lock;
+};
+
+void __cpuinit init_call_single_data(void)
+{
+ int i;
+
+ for_each_possible_cpu(i) {
+ struct call_single_queue *q = &per_cpu(call_single_queue, i);
+
+ spin_lock_init(&q->lock);
+ INIT_LIST_HEAD(&q->list);
+ }
+}
+
+static void csd_flag_wait(struct call_single_data *data)
+{
+ /* Wait for response */
+ do {
+ /*
+ * We need to see the flags store in the IPI handler
+ */
+ smp_mb();
+ if (!(data->flags & CSD_FLAG_WAIT))
+ break;
+ cpu_relax();
+ } while (1);
+}
+
+/*
+ * 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)
+{
+ struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
+ int wait = data->flags & CSD_FLAG_WAIT, ipi;
+ unsigned long flags;
+
+ spin_lock_irqsave(&dst->lock, flags);
+ ipi = list_empty(&dst->list);
+ list_add_tail(&data->list, &dst->list);
+ spin_unlock_irqrestore(&dst->lock, flags);
+
+ if (ipi)
+ arch_send_call_function_single_ipi(cpu);
+
+ if (wait)
+ csd_flag_wait(data);
+}
+
+static void rcu_free_call_data(struct rcu_head *head)
+{
+ struct call_function_data *data;
+
+ data = container_of(head, struct call_function_data, rcu_head);
+
+ kfree(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 = get_cpu();
+
+ /*
+ * It's ok to use list_for_each_rcu() here even though we may delete
+ * 'pos', since list_del_rcu() doesn't clear ->next
+ */
+ rcu_read_lock();
+ list_for_each_entry_rcu(data, &call_function_queue, csd.list) {
+ int refs;
+
+ if (!cpu_isset(cpu, data->cpumask))
+ continue;
+
+ data->csd.func(data->csd.info);
+
+ spin_lock(&data->lock);
+ cpu_clear(cpu, data->cpumask);
+ WARN_ON(data->refs == 0);
+ data->refs--;
+ refs = data->refs;
+ spin_unlock(&data->lock);
+
+ if (refs)
+ continue;
+
+ spin_lock(&call_function_lock);
+ list_del_rcu(&data->csd.list);
+ spin_unlock(&call_function_lock);
+
+ if (data->csd.flags & CSD_FLAG_WAIT) {
+ /*
+ * serialize stores to data with the flag clear
+ * and wakeup
+ */
+ smp_wmb();
+ data->csd.flags &= ~CSD_FLAG_WAIT;
+ } else
+ call_rcu(&data->rcu_head, rcu_free_call_data);
+ }
+ rcu_read_unlock();
+
+ put_cpu();
+}
+
+/*
+ * 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);
+ LIST_HEAD(list);
+
+ /*
+ * Need to see other stores to list head for checking whether
+ * list is empty without holding q->lock
+ */
+ smp_mb();
+ while (!list_empty(&q->list)) {
+ unsigned int data_flags;
+
+ spin_lock(&q->lock);
+ list_replace_init(&q->list, &list);
+ 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);
+
+ if (data_flags & CSD_FLAG_WAIT) {
+ smp_wmb();
+ data->flags &= ~CSD_FLAG_WAIT;
+ } else if (data_flags & CSD_FLAG_ALLOC)
+ kfree(data);
+ }
+ /*
+ * See comment on outer loop
+ */
+ smp_mb();
+ }
+}
+
+/*
+ * 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.
+ * @retry: Unused
+ * @wait: If true, wait until function has completed on other CPUs.
+ *
+ * Returns 0 on success, else a negative status code. Note that @wait
+ * will be implicitly turned on in case of allocation failures, since
+ * we fall back to on-stack allocation.
+ */
+int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
+ int retry, int wait)
+{
+ struct call_single_data d;
+ unsigned long flags;
+ /* prevent preemption and reschedule on another processor */
+ int me = get_cpu();
+
+ /* Can deadlock when called with interrupts disabled */
+ WARN_ON(irqs_disabled());
+
+ if (cpu == me) {
+ local_irq_save(flags);
+ func(info);
+ local_irq_restore(flags);
+ } else {
+ struct call_single_data *data = NULL;
+
+ if (!wait) {
+ data = kmalloc(sizeof(*data), GFP_ATOMIC);
+ if (data)
+ data->flags = CSD_FLAG_ALLOC;
+ }
+ if (!data) {
+ data = &d;
+ data->flags = CSD_FLAG_WAIT;
+ }
+
+ data->func = func;
+ data->info = info;
+ generic_exec_single(cpu, data);
+ }
+
+ put_cpu();
+ return 0;
+}
+EXPORT_SYMBOL(smp_call_function_single);
+
+/**
+ * __smp_call_function_single(): Run a function on another CPU
+ * @cpu: The CPU to run on.
+ * @data: Pre-allocated and setup data structure
+ *
+ * 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)
+{
+ /* Can deadlock when called with interrupts disabled */
+ WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());
+
+ generic_exec_single(cpu, data);
+}
+
+/**
+ * smp_call_function_mask(): Run a function on a set of other CPUs.
+ * @mask: The set of cpus to 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 (atomically) until function has completed on other CPUs.
+ *
+ * Returns 0 on success, else a negative status code.
+ *
+ * If @wait is true, then returns once @func has returned. Note that @wait
+ * will be implicitly turned on in case of allocation failures, since
+ * we fall back to on-stack allocation.
+ *
+ * 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.
+ */
+int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
+ int wait)
+{
+ struct call_function_data d;
+ struct call_function_data *data = NULL;
+ cpumask_t allbutself;
+ unsigned long flags;
+ int cpu, num_cpus;
+
+ /* Can deadlock when called with interrupts disabled */
+ WARN_ON(irqs_disabled());
+
+ cpu = smp_processor_id();
+ allbutself = cpu_online_map;
+ cpu_clear(cpu, allbutself);
+ cpus_and(mask, mask, allbutself);
+ num_cpus = cpus_weight(mask);
+
+ /*
+ * If zero CPUs, return. If just a single CPU, turn this request
+ * into a targetted single call instead since it's faster.
+ */
+ if (!num_cpus)
+ return 0;
+ else if (num_cpus == 1) {
+ cpu = first_cpu(mask);
+ return smp_call_function_single(cpu, func, info, 0, wait);
+ }
+
+ if (!wait) {
+ data = kmalloc(sizeof(*data), GFP_ATOMIC);
+ if (data)
+ data->csd.flags = CSD_FLAG_ALLOC;
+ }
+ if (!data) {
+ data = &d;
+ data->csd.flags = CSD_FLAG_WAIT;
+ }
+
+ spin_lock_init(&data->lock);
+ data->csd.func = func;
+ data->csd.info = info;
+ data->refs = num_cpus;
+ data->cpumask = mask;
+
+ spin_lock_irqsave(&call_function_lock, flags);
+ list_add_tail_rcu(&data->csd.list, &call_function_queue);
+ spin_unlock_irqrestore(&call_function_lock, flags);
+
+ /* Send a message to all CPUs in the map */
+ arch_send_call_function_ipi(mask);
+
+ /* optionally wait for the CPUs to complete */
+ if (wait)
+ csd_flag_wait(&data->csd);
+
+ return 0;
+}
+EXPORT_SYMBOL(smp_call_function_mask);
+
+/**
+ * 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.
+ * @natomic: Unused
+ * @wait: If true, wait (atomically) until function has completed on other CPUs.
+ *
+ * Returns 0 on success, else a negative status code.
+ *
+ * If @wait is true, then returns once @func has returned; otherwise
+ * it returns just before the target cpu calls @func. In case of allocation
+ * failure, @wait will be implicitly turned on.
+ *
+ * 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(void (*func)(void *), void *info, int natomic, int wait)
+{
+ int ret;
+
+ preempt_disable();
+ ret = smp_call_function_mask(cpu_online_map, func, info, wait);
+ preempt_enable();
+ return ret;
+}
+EXPORT_SYMBOL(smp_call_function);
+
+void ipi_call_lock(void)
+{
+ spin_lock(&call_function_lock);
+}
+
+void ipi_call_unlock(void)
+{
+ spin_unlock(&call_function_lock);
+}
+
+void ipi_call_lock_irq(void)
+{
+ spin_lock_irq(&call_function_lock);
+}
+
+void ipi_call_unlock_irq(void)
+{
+ spin_unlock_irq(&call_function_lock);
+}