4 files changed, 319 insertions, 76 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 178858492a8..d07c2888396 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -16,6 +16,7 @@
 #include <linux/init.h>
 #include <linux/hash.h>
 #include <linux/list.h>
+#include <linux/cpu.h>
 #include <linux/fs.h>
 
 #include "trace.h"
@@ -301,6 +302,10 @@ struct ring_buffer {
 	struct mutex			mutex;
 
 	struct ring_buffer_per_cpu	**buffers;
+
+#ifdef CONFIG_HOTPLUG
+	struct notifier_block		cpu_notify;
+#endif
 };
 
 struct ring_buffer_iter {
@@ -459,6 +464,11 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
  */
 extern int ring_buffer_page_too_big(void);
 
+#ifdef CONFIG_HOTPLUG
+static int __cpuinit rb_cpu_notify(struct notifier_block *self,
+				   unsigned long action, void *hcpu);
+#endif
+
 /**
  * ring_buffer_alloc - allocate a new ring_buffer
  * @size: the size in bytes per cpu that is needed.
@@ -496,7 +506,8 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
 	if (buffer->pages == 1)
 		buffer->pages++;
 
-	cpumask_copy(buffer->cpumask, cpu_possible_mask);
+	get_online_cpus();
+	cpumask_copy(buffer->cpumask, cpu_online_mask);
 	buffer->cpus = nr_cpu_ids;
 
 	bsize = sizeof(void *) * nr_cpu_ids;
@@ -512,6 +523,13 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
 			goto fail_free_buffers;
 	}
 
+#ifdef CONFIG_HOTPLUG
+	buffer->cpu_notify.notifier_call = rb_cpu_notify;
+	buffer->cpu_notify.priority = 0;
+	register_cpu_notifier(&buffer->cpu_notify);
+#endif
+
+	put_online_cpus();
 	mutex_init(&buffer->mutex);
 
 	return buffer;
@@ -525,6 +543,7 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
 
  fail_free_cpumask:
 	free_cpumask_var(buffer->cpumask);
+	put_online_cpus();
 
  fail_free_buffer:
 	kfree(buffer);
@@ -541,9 +560,17 @@ ring_buffer_free(struct ring_buffer *buffer)
 {
 	int cpu;
 
+	get_online_cpus();
+
+#ifdef CONFIG_HOTPLUG
+	unregister_cpu_notifier(&buffer->cpu_notify);
+#endif
+
 	for_each_buffer_cpu(buffer, cpu)
 		rb_free_cpu_buffer(buffer->buffers[cpu]);
 
+	put_online_cpus();
+
 	free_cpumask_var(buffer->cpumask);
 
 	kfree(buffer);
@@ -649,16 +676,15 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 		return size;
 
 	mutex_lock(&buffer->mutex);
+	get_online_cpus();
 
 	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 
 	if (size < buffer_size) {
 
 		/* easy case, just free pages */
-		if (RB_WARN_ON(buffer, nr_pages >= buffer->pages)) {
-			mutex_unlock(&buffer->mutex);
-			return -1;
-		}
+		if (RB_WARN_ON(buffer, nr_pages >= buffer->pages))
+			goto out_fail;
 
 		rm_pages = buffer->pages - nr_pages;
 
@@ -677,10 +703,8 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 	 * add these pages to the cpu_buffers. Otherwise we just free
 	 * them all and return -ENOMEM;
 	 */
-	if (RB_WARN_ON(buffer, nr_pages <= buffer->pages)) {
-		mutex_unlock(&buffer->mutex);
-		return -1;
-	}
+	if (RB_WARN_ON(buffer, nr_pages <= buffer->pages))
+		goto out_fail;
 
 	new_pages = nr_pages - buffer->pages;
 
@@ -705,13 +729,12 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 		rb_insert_pages(cpu_buffer, &pages, new_pages);
 	}
 
-	if (RB_WARN_ON(buffer, !list_empty(&pages))) {
-		mutex_unlock(&buffer->mutex);
-		return -1;
-	}
+	if (RB_WARN_ON(buffer, !list_empty(&pages)))
+		goto out_fail;
 
  out:
 	buffer->pages = nr_pages;
+	put_online_cpus();
 	mutex_unlock(&buffer->mutex);
 
 	return size;
@@ -721,8 +744,18 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 		list_del_init(&bpage->list);
 		free_buffer_page(bpage);
 	}
+	put_online_cpus();
 	mutex_unlock(&buffer->mutex);
 	return -ENOMEM;
+
+	/*
+	 * Something went totally wrong, and we are too paranoid
+	 * to even clean up the mess.
+	 */
+ out_fail:
+	put_online_cpus();
+	mutex_unlock(&buffer->mutex);
+	return -1;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_resize);
 
@@ -1528,11 +1561,15 @@ void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 
+	get_online_cpus();
+
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return;
+		goto out;
 
 	cpu_buffer = buffer->buffers[cpu];
 	atomic_inc(&cpu_buffer->record_disabled);
+ out:
+	put_online_cpus();
 }
 EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
 
@@ -1548,11 +1585,15 @@ void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 
+	get_online_cpus();
+
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return;
+		goto out;
 
 	cpu_buffer = buffer->buffers[cpu];
 	atomic_dec(&cpu_buffer->record_disabled);
+ out:
+	put_online_cpus();
 }
 EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
 
@@ -1564,12 +1605,19 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
 unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long ret = 0;
+
+	get_online_cpus();
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return 0;
+		goto out;
 
 	cpu_buffer = buffer->buffers[cpu];
-	return cpu_buffer->entries;
+	ret = cpu_buffer->entries;
+ out:
+	put_online_cpus();
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
 
@@ -1581,12 +1629,19 @@ EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
 unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long ret = 0;
+
+	get_online_cpus();
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return 0;
+		goto out;
 
 	cpu_buffer = buffer->buffers[cpu];
-	return cpu_buffer->overrun;
+	ret = cpu_buffer->overrun;
+ out:
+	put_online_cpus();
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
 
@@ -1603,12 +1658,16 @@ unsigned long ring_buffer_entries(struct ring_buffer *buffer)
 	unsigned long entries = 0;
 	int cpu;
 
+	get_online_cpus();
+
 	/* if you care about this being correct, lock the buffer */
 	for_each_buffer_cpu(buffer, cpu) {
 		cpu_buffer = buffer->buffers[cpu];
 		entries += cpu_buffer->entries;
 	}
 
+	put_online_cpus();
+
 	return entries;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_entries);
@@ -1626,12 +1685,16 @@ unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
 	unsigned long overruns = 0;
 	int cpu;
 
+	get_online_cpus();
+
 	/* if you care about this being correct, lock the buffer */
 	for_each_buffer_cpu(buffer, cpu) {
 		cpu_buffer = buffer->buffers[cpu];
 		overruns += cpu_buffer->overrun;
 	}
 
+	put_online_cpus();
+
 	return overruns;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_overruns);
@@ -1663,9 +1726,14 @@ static void rb_iter_reset(struct ring_buffer_iter *iter)
  */
 void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
 {
-	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
+	struct ring_buffer_per_cpu *cpu_buffer;
 	unsigned long flags;
 
+	if (!iter)
+		return;
+
+	cpu_buffer = iter->cpu_buffer;
+
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 	rb_iter_reset(iter);
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
@@ -1900,9 +1968,6 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
 	struct buffer_page *reader;
 	int nr_loops = 0;
 
-	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return NULL;
-
 	cpu_buffer = buffer->buffers[cpu];
 
  again:
@@ -2028,13 +2093,21 @@ struct ring_buffer_event *
 ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
-	struct ring_buffer_event *event;
+	struct ring_buffer_event *event = NULL;
 	unsigned long flags;
 
+	get_online_cpus();
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		goto out;
+
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 	event = rb_buffer_peek(buffer, cpu, ts);
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+ out:
+	put_online_cpus();
+
 	return event;
 }
 
@@ -2071,24 +2144,31 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 struct ring_buffer_event *
 ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
 {
-	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
-	struct ring_buffer_event *event;
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct ring_buffer_event *event = NULL;
 	unsigned long flags;
 
+	/* might be called in atomic */
+	preempt_disable();
+
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return NULL;
+		goto out;
 
+	cpu_buffer = buffer->buffers[cpu];
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
 	event = rb_buffer_peek(buffer, cpu, ts);
 	if (!event)
-		goto out;
+		goto out_unlock;
 
 	rb_advance_reader(cpu_buffer);
 
- out:
+ out_unlock:
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+ out:
+	preempt_enable();
+
 	return event;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_consume);
@@ -2109,15 +2189,17 @@ struct ring_buffer_iter *
 ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
-	struct ring_buffer_iter *iter;
+	struct ring_buffer_iter *iter = NULL;
 	unsigned long flags;
 
+	get_online_cpus();
+
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return NULL;
+		goto out;
 
 	iter = kmalloc(sizeof(*iter), GFP_KERNEL);
 	if (!iter)
-		return NULL;
+		goto out;
 
 	cpu_buffer = buffer->buffers[cpu];
 
@@ -2132,6 +2214,9 @@ ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
 	__raw_spin_unlock(&cpu_buffer->lock);
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+ out:
+	put_online_cpus();
+
 	return iter;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_read_start);
@@ -2224,9 +2309,13 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
 	unsigned long flags;
+	int resched;
+
+	/* Can't use get_online_cpus because this can be in atomic */
+	resched = ftrace_preempt_disable();
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return;
+		goto out;
 
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
@@ -2237,6 +2326,8 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
 	__raw_spin_unlock(&cpu_buffer->lock);
 
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+ out:
+	ftrace_preempt_enable(resched);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
 
@@ -2246,10 +2337,16 @@ EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
  */
 void ring_buffer_reset(struct ring_buffer *buffer)
 {
+	int resched;
 	int cpu;
 
+	/* Can't use get_online_cpus because this can be in atomic */
+	resched = ftrace_preempt_disable();
+
 	for_each_buffer_cpu(buffer, cpu)
 		ring_buffer_reset_cpu(buffer, cpu);
+
+	ftrace_preempt_enable(resched);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_reset);
 
@@ -2262,12 +2359,17 @@ int ring_buffer_empty(struct ring_buffer *buffer)
 	struct ring_buffer_per_cpu *cpu_buffer;
 	int cpu;
 
+	get_online_cpus();
+
 	/* yes this is racy, but if you don't like the race, lock the buffer */
 	for_each_buffer_cpu(buffer, cpu) {
 		cpu_buffer = buffer->buffers[cpu];
 		if (!rb_per_cpu_empty(cpu_buffer))
 			return 0;
 	}
+
+	put_online_cpus();
+
 	return 1;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_empty);
@@ -2280,12 +2382,20 @@ EXPORT_SYMBOL_GPL(ring_buffer_empty);
 int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
+	int ret = 1;
+
+	get_online_cpus();
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return 1;
+		goto out;
 
 	cpu_buffer = buffer->buffers[cpu];
-	return rb_per_cpu_empty(cpu_buffer);
+	ret = rb_per_cpu_empty(cpu_buffer);
+
+ out:
+	put_online_cpus();
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
 
@@ -2304,32 +2414,37 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 {
 	struct ring_buffer_per_cpu *cpu_buffer_a;
 	struct ring_buffer_per_cpu *cpu_buffer_b;
+	int ret = -EINVAL;
+
+	get_online_cpus();
 
 	if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
 	    !cpumask_test_cpu(cpu, buffer_b->cpumask))
-		return -EINVAL;
+		goto out;
 
 	/* At least make sure the two buffers are somewhat the same */
 	if (buffer_a->pages != buffer_b->pages)
-		return -EINVAL;
+		goto out;
+
+	ret = -EAGAIN;
 
 	if (ring_buffer_flags != RB_BUFFERS_ON)
-		return -EAGAIN;
+		goto out;
 
 	if (atomic_read(&buffer_a->record_disabled))
-		return -EAGAIN;
+		goto out;
 
 	if (atomic_read(&buffer_b->record_disabled))
-		return -EAGAIN;
+		goto out;
 
 	cpu_buffer_a = buffer_a->buffers[cpu];
 	cpu_buffer_b = buffer_b->buffers[cpu];
 
 	if (atomic_read(&cpu_buffer_a->record_disabled))
-		return -EAGAIN;
+		goto out;
 
 	if (atomic_read(&cpu_buffer_b->record_disabled))
-		return -EAGAIN;
+		goto out;
 
 	/*
 	 * We can't do a synchronize_sched here because this
@@ -2349,7 +2464,11 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 	atomic_dec(&cpu_buffer_a->record_disabled);
 	atomic_dec(&cpu_buffer_b->record_disabled);
 
-	return 0;
+	ret = 0;
+out:
+	put_online_cpus();
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
 
@@ -2464,27 +2583,32 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
 	u64 save_timestamp;
 	int ret = -1;
 
+	get_online_cpus();
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		goto out;
+
 	/*
 	 * If len is not big enough to hold the page header, then
 	 * we can not copy anything.
 	 */
 	if (len <= BUF_PAGE_HDR_SIZE)
-		return -1;
+		goto out;
 
 	len -= BUF_PAGE_HDR_SIZE;
 
 	if (!data_page)
-		return -1;
+		goto out;
 
 	bpage = *data_page;
 	if (!bpage)
-		return -1;
+		goto out;
 
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
 	reader = rb_get_reader_page(cpu_buffer);
 	if (!reader)
-		goto out;
+		goto out_unlock;
 
 	event = rb_reader_event(cpu_buffer);
 
@@ -2506,7 +2630,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
 		unsigned int size;
 
 		if (full)
-			goto out;
+			goto out_unlock;
 
 		if (len > (commit - read))
 			len = (commit - read);
@@ -2514,7 +2638,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
 		size = rb_event_length(event);
 
 		if (len < size)
-			goto out;
+			goto out_unlock;
 
 		/* save the current timestamp, since the user will need it */
 		save_timestamp = cpu_buffer->read_stamp;
@@ -2553,9 +2677,12 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
 	}
 	ret = read;
 
- out:
+ out_unlock:
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+ out:
+	put_online_cpus();
+
 	return ret;
 }
 
@@ -2629,3 +2756,42 @@ static __init int rb_init_debugfs(void)
 }
 
 fs_initcall(rb_init_debugfs);
+
+#ifdef CONFIG_HOTPLUG
+static int __cpuinit rb_cpu_notify(struct notifier_block *self,
+				   unsigned long action, void *hcpu)
+{
+	struct ring_buffer *buffer =
+		container_of(self, struct ring_buffer, cpu_notify);
+	long cpu = (long)hcpu;
+
+	switch (action) {
+	case CPU_UP_PREPARE:
+	case CPU_UP_PREPARE_FROZEN:
+		if (cpu_isset(cpu, *buffer->cpumask))
+			return NOTIFY_OK;
+
+		buffer->buffers[cpu] =
+			rb_allocate_cpu_buffer(buffer, cpu);
+		if (!buffer->buffers[cpu]) {
+			WARN(1, "failed to allocate ring buffer on CPU %ld\n",
+			     cpu);
+			return NOTIFY_OK;
+		}
+		smp_wmb();
+		cpu_set(cpu, *buffer->cpumask);
+		break;
+	case CPU_DOWN_PREPARE:
+	case CPU_DOWN_PREPARE_FROZEN:
+		/*
+		 * Do nothing.
+		 *  If we were to free the buffer, then the user would
+		 *  lose any trace that was in the buffer.
+		 */
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+#endif
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5c9c6d90705..c3946a6df34 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -45,6 +45,12 @@ unsigned long __read_mostly	tracing_max_latency;
 unsigned long __read_mostly	tracing_thresh;
 
 /*
+ * On boot up, the ring buffer is set to the minimum size, so that
+ * we do not waste memory on systems that are not using tracing.
+ */
+static int ring_buffer_expanded;
+
+/*
  * We need to change this state when a selftest is running.
  * A selftest will lurk into the ring-buffer to count the
  * entries inserted during the selftest although some concurrent
@@ -128,6 +134,8 @@ static int __init set_ftrace(char *str)
 {
 	strncpy(bootup_tracer_buf, str, BOOTUP_TRACER_SIZE);
 	default_bootup_tracer = bootup_tracer_buf;
+	/* We are using ftrace early, expand it */
+	ring_buffer_expanded = 1;
 	return 1;
 }
 __setup("ftrace=", set_ftrace);
@@ -1658,6 +1666,19 @@ static int trace_empty(struct trace_iterator *iter)
 {
 	int cpu;
 
+	/* If we are looking at one CPU buffer, only check that one */
+	if (iter->cpu_file != TRACE_PIPE_ALL_CPU) {
+		cpu = iter->cpu_file;
+		if (iter->buffer_iter[cpu]) {
+			if (!ring_buffer_iter_empty(iter->buffer_iter[cpu]))
+				return 0;
+		} else {
+			if (!ring_buffer_empty_cpu(iter->tr->buffer, cpu))
+				return 0;
+		}
+		return 1;
+	}
+
 	for_each_tracing_cpu(cpu) {
 		if (iter->buffer_iter[cpu]) {
 			if (!ring_buffer_iter_empty(iter->buffer_iter[cpu]))
@@ -1784,17 +1805,11 @@ __tracing_open(struct inode *inode, struct file *file)
 
 			iter->buffer_iter[cpu] =
 				ring_buffer_read_start(iter->tr->buffer, cpu);
-
-			if (!iter->buffer_iter[cpu])
-				goto fail_buffer;
 		}
 	} else {
 		cpu = iter->cpu_file;
 		iter->buffer_iter[cpu] =
 				ring_buffer_read_start(iter->tr->buffer, cpu);
-
-		if (!iter->buffer_iter[cpu])
-			goto fail;
 	}
 
 	/* TODO stop tracer */
@@ -2315,6 +2330,60 @@ int tracer_init(struct tracer *t, struct trace_array *tr)
 	return t->init(tr);
 }
 
+static int tracing_resize_ring_buffer(unsigned long size)
+{
+	int ret;
+
+	/*
+	 * If kernel or user changes the size of the ring buffer
+	 * it get completed.
+	 */
+	ring_buffer_expanded = 1;
+
+	ret = ring_buffer_resize(global_trace.buffer, size);
+	if (ret < 0)
+		return ret;
+
+	ret = ring_buffer_resize(max_tr.buffer, size);
+	if (ret < 0) {
+		int r;
+
+		r = ring_buffer_resize(global_trace.buffer,
+				       global_trace.entries);
+		if (r < 0) {
+			/* AARGH! We are left with different
+			 * size max buffer!!!! */
+			WARN_ON(1);
+			tracing_disabled = 1;
+		}
+		return ret;
+	}
+
+	global_trace.entries = size;
+
+	return ret;
+}
+
+/**
+ * tracing_update_buffers - used by tracing facility to expand ring buffers
+ *
+ * To save on memory when the tracing is never used on a system with it
+ * configured in. The ring buffers are set to a minimum size. But once
+ * a user starts to use the tracing facility, then they need to grow
+ * to their default size.
+ *
+ * This function is to be called when a tracer is about to be used.
+ */
+int tracing_update_buffers(void)
+{
+	int ret = 0;
+
+	if (!ring_buffer_expanded)
+		ret = tracing_resize_ring_buffer(trace_buf_size);
+
+	return ret;
+}
+
 struct trace_option_dentry;
 
 static struct trace_option_dentry *
@@ -2330,6 +2399,13 @@ static int tracing_set_tracer(const char *buf)
 	struct tracer *t;
 	int ret = 0;
 
+	if (!ring_buffer_expanded) {
+		ret = tracing_resize_ring_buffer(trace_buf_size);
+		if (ret < 0)
+			return ret;
+		ret = 0;
+	}
+
 	mutex_lock(&trace_types_lock);
 	for (t = trace_types; t; t = t->next) {
 		if (strcmp(t->name, buf) == 0)
@@ -2903,28 +2979,11 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
 	val <<= 10;
 
 	if (val != global_trace.entries) {
-		ret = ring_buffer_resize(global_trace.buffer, val);
-		if (ret < 0) {
-			cnt = ret;
-			goto out;
-		}
-
-		ret = ring_buffer_resize(max_tr.buffer, val);
+		ret = tracing_resize_ring_buffer(val);
 		if (ret < 0) {
-			int r;
 			cnt = ret;
-			r = ring_buffer_resize(global_trace.buffer,
-					       global_trace.entries);
-			if (r < 0) {
-				/* AARGH! We are left with different
-				 * size max buffer!!!! */
-				WARN_ON(1);
-				tracing_disabled = 1;
-			}
 			goto out;
 		}
-
-		global_trace.entries = val;
 	}
 
 	filp->f_pos += cnt;
@@ -3916,6 +3975,7 @@ void ftrace_dump(void)
 __init static int tracer_alloc_buffers(void)
 {
 	struct trace_array_cpu *data;
+	int ring_buf_size;
 	int i;
 	int ret = -ENOMEM;
 
@@ -3928,12 +3988,18 @@ __init static int tracer_alloc_buffers(void)
 	if (!alloc_cpumask_var(&tracing_reader_cpumask, GFP_KERNEL))
 		goto out_free_tracing_cpumask;
 
+	/* To save memory, keep the ring buffer size to its minimum */
+	if (ring_buffer_expanded)
+		ring_buf_size = trace_buf_size;
+	else
+		ring_buf_size = 1;
+
 	cpumask_copy(tracing_buffer_mask, cpu_possible_mask);
 	cpumask_copy(tracing_cpumask, cpu_all_mask);
 	cpumask_clear(tracing_reader_cpumask);
 
 	/* TODO: make the number of buffers hot pluggable with CPUS */
-	global_trace.buffer = ring_buffer_alloc(trace_buf_size,
+	global_trace.buffer = ring_buffer_alloc(ring_buf_size,
 						   TRACE_BUFFER_FLAGS);
 	if (!global_trace.buffer) {
 		printk(KERN_ERR "tracer: failed to allocate ring buffer!\n");
@@ -3944,7 +4010,7 @@ __init static int tracer_alloc_buffers(void)
 
 
 #ifdef CONFIG_TRACER_MAX_TRACE
-	max_tr.buffer = ring_buffer_alloc(trace_buf_size,
+	max_tr.buffer = ring_buffer_alloc(ring_buf_size,
 					     TRACE_BUFFER_FLAGS);
 	if (!max_tr.buffer) {
 		printk(KERN_ERR "tracer: failed to allocate max ring buffer!\n");
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index c5e1d8865fe..336324d717f 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -737,6 +737,9 @@ static inline void trace_branch_disable(void)
 }
 #endif /* CONFIG_BRANCH_TRACER */
 
+/* set ring buffers to default size if not already done so */
+int tracing_update_buffers(void);
+
 /* trace event type bit fields, not numeric */
 enum {
 	TRACE_EVENT_TYPE_PRINTF		= 1,
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 769dfd00fc8..ca624df7359 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -141,6 +141,10 @@ ftrace_event_write(struct file *file, const char __user *ubuf,
 	if (!cnt || cnt < 0)
 		return 0;
 
+	ret = tracing_update_buffers();
+	if (ret < 0)
+		return ret;
+
 	ret = get_user(ch, ubuf++);
 	if (ret)
 		return ret;
@@ -331,6 +335,10 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	if (ret < 0)
 		return ret;
 
+	ret = tracing_update_buffers();
+	if (ret < 0)
+		return ret;
+
 	switch (val) {
 	case 0:
 	case 1: