1 files changed, 421 insertions, 164 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index cf8d11e91efd..6420cda62336 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -23,6 +23,8 @@
 #include <asm/local.h>
 #include "trace.h"
 
+static void update_pages_handler(struct work_struct *work);
+
 /*
  * The ring buffer header is special. We must manually up keep it.
  */
@@ -449,6 +451,7 @@ struct ring_buffer_per_cpu {
 	raw_spinlock_t			reader_lock;	/* serialize readers */
 	arch_spinlock_t			lock;
 	struct lock_class_key		lock_key;
+	unsigned int			nr_pages;
 	struct list_head		*pages;
 	struct buffer_page		*head_page;	/* read from head */
 	struct buffer_page		*tail_page;	/* write to tail */
@@ -466,13 +469,18 @@ struct ring_buffer_per_cpu {
 	unsigned long			read_bytes;
 	u64				write_stamp;
 	u64				read_stamp;
+	/* ring buffer pages to update, > 0 to add, < 0 to remove */
+	int				nr_pages_to_update;
+	struct list_head		new_pages; /* new pages to add */
+	struct work_struct		update_pages_work;
+	struct completion		update_done;
 };
 
 struct ring_buffer {
-	unsigned			pages;
 	unsigned			flags;
 	int				cpus;
 	atomic_t			record_disabled;
+	atomic_t			resize_disabled;
 	cpumask_var_t			cpumask;
 
 	struct lock_class_key		*reader_lock_key;
@@ -937,6 +945,10 @@ static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
 	struct list_head *head = cpu_buffer->pages;
 	struct buffer_page *bpage, *tmp;
 
+	/* Reset the head page if it exists */
+	if (cpu_buffer->head_page)
+		rb_set_head_page(cpu_buffer);
+
 	rb_head_page_deactivate(cpu_buffer);
 
 	if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
@@ -963,14 +975,10 @@ static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
 	return 0;
 }
 
-static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
-			     unsigned nr_pages)
+static int __rb_allocate_pages(int nr_pages, struct list_head *pages, int cpu)
 {
+	int i;
 	struct buffer_page *bpage, *tmp;
-	LIST_HEAD(pages);
-	unsigned i;
-
-	WARN_ON(!nr_pages);
 
 	for (i = 0; i < nr_pages; i++) {
 		struct page *page;
@@ -981,15 +989,13 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 		 */
 		bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
 				    GFP_KERNEL | __GFP_NORETRY,
-				    cpu_to_node(cpu_buffer->cpu));
+				    cpu_to_node(cpu));
 		if (!bpage)
 			goto free_pages;
 
-		rb_check_bpage(cpu_buffer, bpage);
+		list_add(&bpage->list, pages);
 
-		list_add(&bpage->list, &pages);
-
-		page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu),
+		page = alloc_pages_node(cpu_to_node(cpu),
 					GFP_KERNEL | __GFP_NORETRY, 0);
 		if (!page)
 			goto free_pages;
@@ -997,6 +1003,27 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 		rb_init_page(bpage->page);
 	}
 
+	return 0;
+
+free_pages:
+	list_for_each_entry_safe(bpage, tmp, pages, list) {
+		list_del_init(&bpage->list);
+		free_buffer_page(bpage);
+	}
+
+	return -ENOMEM;
+}
+
+static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
+			     unsigned nr_pages)
+{
+	LIST_HEAD(pages);
+
+	WARN_ON(!nr_pages);
+
+	if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
+		return -ENOMEM;
+
 	/*
 	 * The ring buffer page list is a circular list that does not
 	 * start and end with a list head. All page list items point to
@@ -1005,20 +1032,15 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	cpu_buffer->pages = pages.next;
 	list_del(&pages);
 
+	cpu_buffer->nr_pages = nr_pages;
+
 	rb_check_pages(cpu_buffer);
 
 	return 0;
-
- free_pages:
-	list_for_each_entry_safe(bpage, tmp, &pages, list) {
-		list_del_init(&bpage->list);
-		free_buffer_page(bpage);
-	}
-	return -ENOMEM;
 }
 
 static struct ring_buffer_per_cpu *
-rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
+rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 	struct buffer_page *bpage;
@@ -1035,6 +1057,8 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
 	raw_spin_lock_init(&cpu_buffer->reader_lock);
 	lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
 	cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
+	INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
+	init_completion(&cpu_buffer->update_done);
 
 	bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
 			    GFP_KERNEL, cpu_to_node(cpu));
@@ -1052,7 +1076,7 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
 
 	INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
 
-	ret = rb_allocate_pages(cpu_buffer, buffer->pages);
+	ret = rb_allocate_pages(cpu_buffer, nr_pages);
 	if (ret < 0)
 		goto fail_free_reader;
 
@@ -1113,7 +1137,7 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
 {
 	struct ring_buffer *buffer;
 	int bsize;
-	int cpu;
+	int cpu, nr_pages;
 
 	/* keep it in its own cache line */
 	buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
@@ -1124,14 +1148,14 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
 	if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
 		goto fail_free_buffer;
 
-	buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
+	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 	buffer->flags = flags;
 	buffer->clock = trace_clock_local;
 	buffer->reader_lock_key = key;
 
 	/* need at least two pages */
-	if (buffer->pages < 2)
-		buffer->pages = 2;
+	if (nr_pages < 2)
+		nr_pages = 2;
 
 	/*
 	 * In case of non-hotplug cpu, if the ring-buffer is allocated
@@ -1154,7 +1178,7 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
 
 	for_each_buffer_cpu(buffer, cpu) {
 		buffer->buffers[cpu] =
-			rb_allocate_cpu_buffer(buffer, cpu);
+			rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
 		if (!buffer->buffers[cpu])
 			goto fail_free_buffers;
 	}
@@ -1222,58 +1246,222 @@ void ring_buffer_set_clock(struct ring_buffer *buffer,
 
 static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
 
-static void
-rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
+static inline unsigned long rb_page_entries(struct buffer_page *bpage)
 {
-	struct buffer_page *bpage;
-	struct list_head *p;
-	unsigned i;
+	return local_read(&bpage->entries) & RB_WRITE_MASK;
+}
+
+static inline unsigned long rb_page_write(struct buffer_page *bpage)
+{
+	return local_read(&bpage->write) & RB_WRITE_MASK;
+}
+
+static int
+rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
+{
+	struct list_head *tail_page, *to_remove, *next_page;
+	struct buffer_page *to_remove_page, *tmp_iter_page;
+	struct buffer_page *last_page, *first_page;
+	unsigned int nr_removed;
+	unsigned long head_bit;
+	int page_entries;
+
+	head_bit = 0;
 
 	raw_spin_lock_irq(&cpu_buffer->reader_lock);
-	rb_head_page_deactivate(cpu_buffer);
+	atomic_inc(&cpu_buffer->record_disabled);
+	/*
+	 * We don't race with the readers since we have acquired the reader
+	 * lock. We also don't race with writers after disabling recording.
+	 * This makes it easy to figure out the first and the last page to be
+	 * removed from the list. We unlink all the pages in between including
+	 * the first and last pages. This is done in a busy loop so that we
+	 * lose the least number of traces.
+	 * The pages are freed after we restart recording and unlock readers.
+	 */
+	tail_page = &cpu_buffer->tail_page->list;
 
-	for (i = 0; i < nr_pages; i++) {
-		if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
-			goto out;
-		p = cpu_buffer->pages->next;
-		bpage = list_entry(p, struct buffer_page, list);
-		list_del_init(&bpage->list);
-		free_buffer_page(bpage);
+	/*
+	 * tail page might be on reader page, we remove the next page
+	 * from the ring buffer
+	 */
+	if (cpu_buffer->tail_page == cpu_buffer->reader_page)
+		tail_page = rb_list_head(tail_page->next);
+	to_remove = tail_page;
+
+	/* start of pages to remove */
+	first_page = list_entry(rb_list_head(to_remove->next),
+				struct buffer_page, list);
+
+	for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
+		to_remove = rb_list_head(to_remove)->next;
+		head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
 	}
-	if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
-		goto out;
 
-	rb_reset_cpu(cpu_buffer);
-	rb_check_pages(cpu_buffer);
+	next_page = rb_list_head(to_remove)->next;
 
-out:
+	/*
+	 * Now we remove all pages between tail_page and next_page.
+	 * Make sure that we have head_bit value preserved for the
+	 * next page
+	 */
+	tail_page->next = (struct list_head *)((unsigned long)next_page |
+						head_bit);
+	next_page = rb_list_head(next_page);
+	next_page->prev = tail_page;
+
+	/* make sure pages points to a valid page in the ring buffer */
+	cpu_buffer->pages = next_page;
+
+	/* update head page */
+	if (head_bit)
+		cpu_buffer->head_page = list_entry(next_page,
+						struct buffer_page, list);
+
+	/*
+	 * change read pointer to make sure any read iterators reset
+	 * themselves
+	 */
+	cpu_buffer->read = 0;
+
+	/* pages are removed, resume tracing and then free the pages */
+	atomic_dec(&cpu_buffer->record_disabled);
 	raw_spin_unlock_irq(&cpu_buffer->reader_lock);
+
+	RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
+
+	/* last buffer page to remove */
+	last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
+				list);
+	tmp_iter_page = first_page;
+
+	do {
+		to_remove_page = tmp_iter_page;
+		rb_inc_page(cpu_buffer, &tmp_iter_page);
+
+		/* update the counters */
+		page_entries = rb_page_entries(to_remove_page);
+		if (page_entries) {
+			/*
+			 * If something was added to this page, it was full
+			 * since it is not the tail page. So we deduct the
+			 * bytes consumed in ring buffer from here.
+			 * No need to update overruns, since this page is
+			 * deleted from ring buffer and its entries are
+			 * already accounted for.
+			 */
+			local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
+		}
+
+		/*
+		 * We have already removed references to this list item, just
+		 * free up the buffer_page and its page
+		 */
+		free_buffer_page(to_remove_page);
+		nr_removed--;
+
+	} while (to_remove_page != last_page);
+
+	RB_WARN_ON(cpu_buffer, nr_removed);
+
+	return nr_removed == 0;
 }
 
-static void
-rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
-		struct list_head *pages, unsigned nr_pages)
+static int
+rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
 {
-	struct buffer_page *bpage;
-	struct list_head *p;
-	unsigned i;
+	struct list_head *pages = &cpu_buffer->new_pages;
+	int retries, success;
 
 	raw_spin_lock_irq(&cpu_buffer->reader_lock);
-	rb_head_page_deactivate(cpu_buffer);
+	/*
+	 * We are holding the reader lock, so the reader page won't be swapped
+	 * in the ring buffer. Now we are racing with the writer trying to
+	 * move head page and the tail page.
+	 * We are going to adapt the reader page update process where:
+	 * 1. We first splice the start and end of list of new pages between
+	 *    the head page and its previous page.
+	 * 2. We cmpxchg the prev_page->next to point from head page to the
+	 *    start of new pages list.
+	 * 3. Finally, we update the head->prev to the end of new list.
+	 *
+	 * We will try this process 10 times, to make sure that we don't keep
+	 * spinning.
+	 */
+	retries = 10;
+	success = 0;
+	while (retries--) {
+		struct list_head *head_page, *prev_page, *r;
+		struct list_head *last_page, *first_page;
+		struct list_head *head_page_with_bit;
 
-	for (i = 0; i < nr_pages; i++) {
-		if (RB_WARN_ON(cpu_buffer, list_empty(pages)))
-			goto out;
-		p = pages->next;
-		bpage = list_entry(p, struct buffer_page, list);
-		list_del_init(&bpage->list);
-		list_add_tail(&bpage->list, cpu_buffer->pages);
+		head_page = &rb_set_head_page(cpu_buffer)->list;
+		prev_page = head_page->prev;
+
+		first_page = pages->next;
+		last_page  = pages->prev;
+
+		head_page_with_bit = (struct list_head *)
+				     ((unsigned long)head_page | RB_PAGE_HEAD);
+
+		last_page->next = head_page_with_bit;
+		first_page->prev = prev_page;
+
+		r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
+
+		if (r == head_page_with_bit) {
+			/*
+			 * yay, we replaced the page pointer to our new list,
+			 * now, we just have to update to head page's prev
+			 * pointer to point to end of list
+			 */
+			head_page->prev = last_page;
+			success = 1;
+			break;
+		}
 	}
-	rb_reset_cpu(cpu_buffer);
-	rb_check_pages(cpu_buffer);
 
-out:
+	if (success)
+		INIT_LIST_HEAD(pages);
+	/*
+	 * If we weren't successful in adding in new pages, warn and stop
+	 * tracing
+	 */
+	RB_WARN_ON(cpu_buffer, !success);
 	raw_spin_unlock_irq(&cpu_buffer->reader_lock);
+
+	/* free pages if they weren't inserted */
+	if (!success) {
+		struct buffer_page *bpage, *tmp;
+		list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
+					 list) {
+			list_del_init(&bpage->list);
+			free_buffer_page(bpage);
+		}
+	}
+	return success;
+}
+
+static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	int success;
+
+	if (cpu_buffer->nr_pages_to_update > 0)
+		success = rb_insert_pages(cpu_buffer);
+	else
+		success = rb_remove_pages(cpu_buffer,
+					-cpu_buffer->nr_pages_to_update);
+
+	if (success)
+		cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
+}
+
+static void update_pages_handler(struct work_struct *work)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
+			struct ring_buffer_per_cpu, update_pages_work);
+	rb_update_pages(cpu_buffer);
+	complete(&cpu_buffer->update_done);
 }
 
 /**
@@ -1283,16 +1471,14 @@ out:
  *
  * Minimum size is 2 * BUF_PAGE_SIZE.
  *
- * Returns -1 on failure.
+ * Returns 0 on success and < 0 on failure.
  */
-int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
+int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
+			int cpu_id)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
-	unsigned nr_pages, rm_pages, new_pages;
-	struct buffer_page *bpage, *tmp;
-	unsigned long buffer_size;
-	LIST_HEAD(pages);
-	int i, cpu;
+	unsigned nr_pages;
+	int cpu, err = 0;
 
 	/*
 	 * Always succeed at resizing a non-existent buffer:
@@ -1302,113 +1488,154 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 
 	size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 	size *= BUF_PAGE_SIZE;
-	buffer_size = buffer->pages * BUF_PAGE_SIZE;
 
 	/* we need a minimum of two pages */
 	if (size < BUF_PAGE_SIZE * 2)
 		size = BUF_PAGE_SIZE * 2;
 
-	if (size == buffer_size)
-		return size;
-
-	atomic_inc(&buffer->record_disabled);
+	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 
-	/* Make sure all writers are done with this buffer. */
-	synchronize_sched();
+	/*
+	 * Don't succeed if resizing is disabled, as a reader might be
+	 * manipulating the ring buffer and is expecting a sane state while
+	 * this is true.
+	 */
+	if (atomic_read(&buffer->resize_disabled))
+		return -EBUSY;
 
+	/* prevent another thread from changing buffer sizes */
 	mutex_lock(&buffer->mutex);
-	get_online_cpus();
-
-	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 
-	if (size < buffer_size) {
+	if (cpu_id == RING_BUFFER_ALL_CPUS) {
+		/* calculate the pages to update */
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
 
-		/* easy case, just free pages */
-		if (RB_WARN_ON(buffer, nr_pages >= buffer->pages))
-			goto out_fail;
+			cpu_buffer->nr_pages_to_update = nr_pages -
+							cpu_buffer->nr_pages;
+			/*
+			 * nothing more to do for removing pages or no update
+			 */
+			if (cpu_buffer->nr_pages_to_update <= 0)
+				continue;
+			/*
+			 * to add pages, make sure all new pages can be
+			 * allocated without receiving ENOMEM
+			 */
+			INIT_LIST_HEAD(&cpu_buffer->new_pages);
+			if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
+						&cpu_buffer->new_pages, cpu)) {
+				/* not enough memory for new pages */
+				err = -ENOMEM;
+				goto out_err;
+			}
+		}
 
-		rm_pages = buffer->pages - nr_pages;
+		get_online_cpus();
+		/*
+		 * Fire off all the required work handlers
+		 * We can't schedule on offline CPUs, but it's not necessary
+		 * since we can change their buffer sizes without any race.
+		 */
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
+			if (!cpu_buffer->nr_pages_to_update)
+				continue;
+
+			if (cpu_online(cpu))
+				schedule_work_on(cpu,
+						&cpu_buffer->update_pages_work);
+			else
+				rb_update_pages(cpu_buffer);
+		}
 
+		/* wait for all the updates to complete */
 		for_each_buffer_cpu(buffer, cpu) {
 			cpu_buffer = buffer->buffers[cpu];
-			rb_remove_pages(cpu_buffer, rm_pages);
+			if (!cpu_buffer->nr_pages_to_update)
+				continue;
+
+			if (cpu_online(cpu))
+				wait_for_completion(&cpu_buffer->update_done);
+			cpu_buffer->nr_pages_to_update = 0;
 		}
-		goto out;
-	}
 
-	/*
-	 * This is a bit more difficult. We only want to add pages
-	 * when we can allocate enough for all CPUs. We do this
-	 * by allocating all the pages and storing them on a local
-	 * link list. If we succeed in our allocation, then we
-	 * 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))
-		goto out_fail;
+		put_online_cpus();
+	} else {
+		cpu_buffer = buffer->buffers[cpu_id];
 
-	new_pages = nr_pages - buffer->pages;
+		if (nr_pages == cpu_buffer->nr_pages)
+			goto out;
 
-	for_each_buffer_cpu(buffer, cpu) {
-		for (i = 0; i < new_pages; i++) {
-			struct page *page;
-			/*
-			 * __GFP_NORETRY flag makes sure that the allocation
-			 * fails gracefully without invoking oom-killer and
-			 * the system is not destabilized.
-			 */
-			bpage = kzalloc_node(ALIGN(sizeof(*bpage),
-						  cache_line_size()),
-					    GFP_KERNEL | __GFP_NORETRY,
-					    cpu_to_node(cpu));
-			if (!bpage)
-				goto free_pages;
-			list_add(&bpage->list, &pages);
-			page = alloc_pages_node(cpu_to_node(cpu),
-						GFP_KERNEL | __GFP_NORETRY, 0);
-			if (!page)
-				goto free_pages;
-			bpage->page = page_address(page);
-			rb_init_page(bpage->page);
+		cpu_buffer->nr_pages_to_update = nr_pages -
+						cpu_buffer->nr_pages;
+
+		INIT_LIST_HEAD(&cpu_buffer->new_pages);
+		if (cpu_buffer->nr_pages_to_update > 0 &&
+			__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
+					    &cpu_buffer->new_pages, cpu_id)) {
+			err = -ENOMEM;
+			goto out_err;
 		}
-	}
 
-	for_each_buffer_cpu(buffer, cpu) {
-		cpu_buffer = buffer->buffers[cpu];
-		rb_insert_pages(cpu_buffer, &pages, new_pages);
-	}
+		get_online_cpus();
 
-	if (RB_WARN_ON(buffer, !list_empty(&pages)))
-		goto out_fail;
+		if (cpu_online(cpu_id)) {
+			schedule_work_on(cpu_id,
+					 &cpu_buffer->update_pages_work);
+			wait_for_completion(&cpu_buffer->update_done);
+		} else
+			rb_update_pages(cpu_buffer);
+
+		cpu_buffer->nr_pages_to_update = 0;
+		put_online_cpus();
+	}
 
  out:
-	buffer->pages = nr_pages;
-	put_online_cpus();
+	/*
+	 * The ring buffer resize can happen with the ring buffer
+	 * enabled, so that the update disturbs the tracing as little
+	 * as possible. But if the buffer is disabled, we do not need
+	 * to worry about that, and we can take the time to verify
+	 * that the buffer is not corrupt.
+	 */
+	if (atomic_read(&buffer->record_disabled)) {
+		atomic_inc(&buffer->record_disabled);
+		/*
+		 * Even though the buffer was disabled, we must make sure
+		 * that it is truly disabled before calling rb_check_pages.
+		 * There could have been a race between checking
+		 * record_disable and incrementing it.
+		 */
+		synchronize_sched();
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
+			rb_check_pages(cpu_buffer);
+		}
+		atomic_dec(&buffer->record_disabled);
+	}
+
 	mutex_unlock(&buffer->mutex);
+	return size;
 
-	atomic_dec(&buffer->record_disabled);
+ out_err:
+	for_each_buffer_cpu(buffer, cpu) {
+		struct buffer_page *bpage, *tmp;
 
-	return size;
+		cpu_buffer = buffer->buffers[cpu];
+		cpu_buffer->nr_pages_to_update = 0;
 
- free_pages:
-	list_for_each_entry_safe(bpage, tmp, &pages, list) {
-		list_del_init(&bpage->list);
-		free_buffer_page(bpage);
-	}
-	put_online_cpus();
-	mutex_unlock(&buffer->mutex);
-	atomic_dec(&buffer->record_disabled);
-	return -ENOMEM;
+		if (list_empty(&cpu_buffer->new_pages))
+			continue;
 
-	/*
-	 * Something went totally wrong, and we are too paranoid
-	 * to even clean up the mess.
-	 */
- out_fail:
-	put_online_cpus();
+		list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
+					list) {
+			list_del_init(&bpage->list);
+			free_buffer_page(bpage);
+		}
+	}
 	mutex_unlock(&buffer->mutex);
-	atomic_dec(&buffer->record_disabled);
-	return -1;
+	return err;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_resize);
 
@@ -1447,21 +1674,11 @@ rb_iter_head_event(struct ring_buffer_iter *iter)
 	return __rb_page_index(iter->head_page, iter->head);
 }
 
-static inline unsigned long rb_page_write(struct buffer_page *bpage)
-{
-	return local_read(&bpage->write) & RB_WRITE_MASK;
-}
-
 static inline unsigned rb_page_commit(struct buffer_page *bpage)
 {
 	return local_read(&bpage->page->commit);
 }
 
-static inline unsigned long rb_page_entries(struct buffer_page *bpage)
-{
-	return local_read(&bpage->entries) & RB_WRITE_MASK;
-}
-
 /* Size is determined by what has been committed */
 static inline unsigned rb_page_size(struct buffer_page *bpage)
 {
@@ -1510,7 +1727,7 @@ rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
 	 * assign the commit to the tail.
 	 */
  again:
-	max_count = cpu_buffer->buffer->pages * 100;
+	max_count = cpu_buffer->nr_pages * 100;
 
 	while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
 		if (RB_WARN_ON(cpu_buffer, !(--max_count)))
@@ -3486,6 +3703,7 @@ ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
 
 	iter->cpu_buffer = cpu_buffer;
 
+	atomic_inc(&buffer->resize_disabled);
 	atomic_inc(&cpu_buffer->record_disabled);
 
 	return iter;
@@ -3548,7 +3766,14 @@ ring_buffer_read_finish(struct ring_buffer_iter *iter)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
 
+	/*
+	 * Ring buffer is disabled from recording, here's a good place
+	 * to check the integrity of the ring buffer. 
+	 */
+	rb_check_pages(cpu_buffer);
+
 	atomic_dec(&cpu_buffer->record_disabled);
+	atomic_dec(&cpu_buffer->buffer->resize_disabled);
 	kfree(iter);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
@@ -3588,9 +3813,18 @@ EXPORT_SYMBOL_GPL(ring_buffer_read);
  * ring_buffer_size - return the size of the ring buffer (in bytes)
  * @buffer: The ring buffer.
  */
-unsigned long ring_buffer_size(struct ring_buffer *buffer)
+unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu)
 {
-	return BUF_PAGE_SIZE * buffer->pages;
+	/*
+	 * Earlier, this method returned
+	 *	BUF_PAGE_SIZE * buffer->nr_pages
+	 * Since the nr_pages field is now removed, we have converted this to
+	 * return the per cpu buffer value.
+	 */
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_size);
 
@@ -3611,6 +3845,7 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 	cpu_buffer->commit_page = cpu_buffer->head_page;
 
 	INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
+	INIT_LIST_HEAD(&cpu_buffer->new_pages);
 	local_set(&cpu_buffer->reader_page->write, 0);
 	local_set(&cpu_buffer->reader_page->entries, 0);
 	local_set(&cpu_buffer->reader_page->page->commit, 0);
@@ -3647,8 +3882,12 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return;
 
+	atomic_inc(&buffer->resize_disabled);
 	atomic_inc(&cpu_buffer->record_disabled);
 
+	/* Make sure all commits have finished */
+	synchronize_sched();
+
 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
 	if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
@@ -3664,6 +3903,7 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
 	atomic_dec(&cpu_buffer->record_disabled);
+	atomic_dec(&buffer->resize_disabled);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
 
@@ -3765,8 +4005,11 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 	    !cpumask_test_cpu(cpu, buffer_b->cpumask))
 		goto out;
 
+	cpu_buffer_a = buffer_a->buffers[cpu];
+	cpu_buffer_b = buffer_b->buffers[cpu];
+
 	/* At least make sure the two buffers are somewhat the same */
-	if (buffer_a->pages != buffer_b->pages)
+	if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
 		goto out;
 
 	ret = -EAGAIN;
@@ -3780,9 +4023,6 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 	if (atomic_read(&buffer_b->record_disabled))
 		goto out;
 
-	cpu_buffer_a = buffer_a->buffers[cpu];
-	cpu_buffer_b = buffer_b->buffers[cpu];
-
 	if (atomic_read(&cpu_buffer_a->record_disabled))
 		goto out;
 
@@ -4071,6 +4311,8 @@ static int rb_cpu_notify(struct notifier_block *self,
 	struct ring_buffer *buffer =
 		container_of(self, struct ring_buffer, cpu_notify);
 	long cpu = (long)hcpu;
+	int cpu_i, nr_pages_same;
+	unsigned int nr_pages;
 
 	switch (action) {
 	case CPU_UP_PREPARE:
@@ -4078,8 +4320,23 @@ static int rb_cpu_notify(struct notifier_block *self,
 		if (cpumask_test_cpu(cpu, buffer->cpumask))
 			return NOTIFY_OK;
 
+		nr_pages = 0;
+		nr_pages_same = 1;
+		/* check if all cpu sizes are same */
+		for_each_buffer_cpu(buffer, cpu_i) {
+			/* fill in the size from first enabled cpu */
+			if (nr_pages == 0)
+				nr_pages = buffer->buffers[cpu_i]->nr_pages;
+			if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
+				nr_pages_same = 0;
+				break;
+			}
+		}
+		/* allocate minimum pages, user can later expand it */
+		if (!nr_pages_same)
+			nr_pages = 2;
 		buffer->buffers[cpu] =
-			rb_allocate_cpu_buffer(buffer, cpu);
+			rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
 		if (!buffer->buffers[cpu]) {
 			WARN(1, "failed to allocate ring buffer on CPU %ld\n",
 			     cpu);