1 files changed, 170 insertions, 14 deletions

diff --git a/kernel/smp.c b/kernel/smp.c
index 4ec30e06998..73a19519355 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -194,23 +194,52 @@ void generic_smp_call_function_interrupt(void)
 	 */
 	list_for_each_entry_rcu(data, &call_function.queue, csd.list) {
 		int refs;
+		smp_call_func_t func;
 
-		if (!cpumask_test_and_clear_cpu(cpu, data->cpumask))
+		/*
+		 * 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;
 
-		data->csd.func(data->csd.info);
+		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) {
-			raw_spin_lock(&call_function.lock);
-			list_del_rcu(&data->csd.list);
-			raw_spin_unlock(&call_function.lock);
-		}
 
 		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);
 	}
 
@@ -421,7 +450,7 @@ void smp_call_function_many(const struct cpumask *mask,
 {
 	struct call_function_data *data;
 	unsigned long flags;
-	int cpu, next_cpu, this_cpu = smp_processor_id();
+	int refs, cpu, next_cpu, this_cpu = smp_processor_id();
 
 	/*
 	 * Can deadlock when called with interrupts disabled.
@@ -430,9 +459,9 @@ void smp_call_function_many(const struct cpumask *mask,
 	 * can't happen.
 	 */
 	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
-		     && !oops_in_progress);
+		     && !oops_in_progress && !early_boot_irqs_disabled);
 
-	/* So, what's a CPU they want? Ignoring this one. */
+	/* 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);
@@ -455,11 +484,48 @@ void smp_call_function_many(const struct cpumask *mask,
 	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);
-	atomic_set(&data->refs, cpumask_weight(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);
 	/*
@@ -468,6 +534,12 @@ void smp_call_function_many(const struct cpumask *mask,
 	 * 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);
 
 	/*
@@ -532,18 +604,102 @@ void ipi_call_unlock_irq(void)
 }
 #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
+ * 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_disable();
+	local_irq_save(flags);
 	func(info);
-	local_irq_enable();
+	local_irq_restore(flags);
 	preempt_enable();
 	return ret;
 }