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>

2 files changed, 384 insertions, 0 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index 1c9938a..9fa5797 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -28,6 +28,7 @@ obj-$(CONFIG_DEBUG_RT_MUTEXES) += rtmutex-debug.o
 obj-$(CONFIG_RT_MUTEX_TESTER) += rtmutex-tester.o
 obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
 obj-$(CONFIG_SMP) += cpu.o spinlock.o
+obj-$(CONFIG_USE_GENERIC_SMP_HELPERS) += smp.o
 obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
 obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
 obj-$(CONFIG_UID16) += uid16.o
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);
+}