2 files changed, 209 insertions, 76 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2d5eb33..27ac37e 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.
  */
@@ -470,12 +472,15 @@ struct ring_buffer_per_cpu {
 	/* 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_completion;
 };
 
 struct ring_buffer {
 	unsigned			flags;
 	int				cpus;
 	atomic_t			record_disabled;
+	atomic_t			resize_disabled;
 	cpumask_var_t			cpumask;
 
 	struct lock_class_key		*reader_lock_key;
@@ -1048,6 +1053,8 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, 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_completion);
 
 	bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
 			    GFP_KERNEL, cpu_to_node(cpu));
@@ -1235,32 +1242,123 @@ void ring_buffer_set_clock(struct ring_buffer *buffer,
 
 static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
 
+static inline unsigned long rb_page_entries(struct buffer_page *bpage)
+{
+	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 void
-rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
+rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
 {
-	struct buffer_page *bpage;
-	struct list_head *p;
-	unsigned i;
+	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);
 }
 
 static void
@@ -1272,6 +1370,8 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	unsigned i;
 
 	raw_spin_lock_irq(&cpu_buffer->reader_lock);
+	/* stop the writers while inserting pages */
+	atomic_inc(&cpu_buffer->record_disabled);
 	rb_head_page_deactivate(cpu_buffer);
 
 	for (i = 0; i < nr_pages; i++) {
@@ -1286,19 +1386,27 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	rb_check_pages(cpu_buffer);
 
 out:
+	atomic_dec(&cpu_buffer->record_disabled);
 	raw_spin_unlock_irq(&cpu_buffer->reader_lock);
 }
 
-static void update_pages_handler(struct ring_buffer_per_cpu *cpu_buffer)
+static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	if (cpu_buffer->nr_pages_to_update > 0)
 		rb_insert_pages(cpu_buffer, &cpu_buffer->new_pages,
 				cpu_buffer->nr_pages_to_update);
 	else
 		rb_remove_pages(cpu_buffer, -cpu_buffer->nr_pages_to_update);
+
 	cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
-	/* reset this value */
-	cpu_buffer->nr_pages_to_update = 0;
+}
+
+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_completion);
 }
 
 /**
@@ -1308,14 +1416,14 @@ static void update_pages_handler(struct ring_buffer_per_cpu *cpu_buffer)
  *
  * 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 cpu_id)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 	unsigned nr_pages;
-	int cpu;
+	int cpu, err = 0;
 
 	/*
 	 * Always succeed at resizing a non-existent buffer:
@@ -1330,15 +1438,18 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
 	if (size < BUF_PAGE_SIZE * 2)
 		size = BUF_PAGE_SIZE * 2;
 
-	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 (cpu_id == RING_BUFFER_ALL_CPUS) {
 		/* calculate the pages to update */
@@ -1347,33 +1458,67 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
 
 			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))
+						&cpu_buffer->new_pages, cpu)) {
 				/* not enough memory for new pages */
-				goto no_mem;
+				err = -ENOMEM;
+				goto out_err;
+			}
+		}
+
+		get_online_cpus();
+		/*
+		 * Fire off all the required work handlers
+		 * Look out for offline CPUs
+		 */
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
+			if (!cpu_buffer->nr_pages_to_update ||
+			    !cpu_online(cpu))
+				continue;
+
+			schedule_work_on(cpu, &cpu_buffer->update_pages_work);
+		}
+		/*
+		 * This loop is for the CPUs that are not online.
+		 * We can't schedule anything on them, 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 ||
+			    cpu_online(cpu))
+				continue;
+
+			rb_update_pages(cpu_buffer);
 		}
 
 		/* wait for all the updates to complete */
 		for_each_buffer_cpu(buffer, cpu) {
 			cpu_buffer = buffer->buffers[cpu];
-			if (cpu_buffer->nr_pages_to_update) {
-				update_pages_handler(cpu_buffer);
-			}
+			if (!cpu_buffer->nr_pages_to_update ||
+			    !cpu_online(cpu))
+				continue;
+
+			wait_for_completion(&cpu_buffer->update_completion);
+			/* reset this value */
+			cpu_buffer->nr_pages_to_update = 0;
 		}
+
+		put_online_cpus();
 	} else {
 		cpu_buffer = buffer->buffers[cpu_id];
+
 		if (nr_pages == cpu_buffer->nr_pages)
 			goto out;
 
@@ -1383,38 +1528,47 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
 		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))
-			goto no_mem;
+					    &cpu_buffer->new_pages, cpu_id)) {
+			err = -ENOMEM;
+			goto out_err;
+		}
 
-		update_pages_handler(cpu_buffer);
+		get_online_cpus();
+
+		if (cpu_online(cpu_id)) {
+			schedule_work_on(cpu_id,
+					 &cpu_buffer->update_pages_work);
+			wait_for_completion(&cpu_buffer->update_completion);
+		} else
+			rb_update_pages(cpu_buffer);
+
+		put_online_cpus();
+		/* reset this value */
+		cpu_buffer->nr_pages_to_update = 0;
 	}
 
  out:
-	put_online_cpus();
 	mutex_unlock(&buffer->mutex);
-
-	atomic_dec(&buffer->record_disabled);
-
 	return size;
 
- no_mem:
+ out_err:
 	for_each_buffer_cpu(buffer, cpu) {
 		struct buffer_page *bpage, *tmp;
+
 		cpu_buffer = buffer->buffers[cpu];
-		/* reset this number regardless */
 		cpu_buffer->nr_pages_to_update = 0;
+
 		if (list_empty(&cpu_buffer->new_pages))
 			continue;
+
 		list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_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;
+	return err;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_resize);
 
@@ -1453,21 +1607,11 @@ 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)
 {
@@ -3492,6 +3636,7 @@ 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;
@@ -3555,6 +3700,7 @@ ring_buffer_read_finish(struct ring_buffer_iter *iter)
 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
 
 	atomic_dec(&cpu_buffer->record_disabled);
+	atomic_dec(&cpu_buffer->buffer->resize_disabled);
 	kfree(iter);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
@@ -3662,8 +3808,12 @@ 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)))
@@ -3679,6 +3829,7 @@ 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);
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d1b3469..dfbd86c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3076,20 +3076,10 @@ static int __tracing_resize_ring_buffer(unsigned long size, int cpu)
 
 static ssize_t tracing_resize_ring_buffer(unsigned long size, int cpu_id)
 {
-	int cpu, ret = size;
+	int ret = size;
 
 	mutex_lock(&trace_types_lock);
 
-	tracing_stop();
-
-	/* disable all cpu buffers */
-	for_each_tracing_cpu(cpu) {
-		if (global_trace.data[cpu])
-			atomic_inc(&global_trace.data[cpu]->disabled);
-		if (max_tr.data[cpu])
-			atomic_inc(&max_tr.data[cpu]->disabled);
-	}
-
 	if (cpu_id != RING_BUFFER_ALL_CPUS) {
 		/* make sure, this cpu is enabled in the mask */
 		if (!cpumask_test_cpu(cpu_id, tracing_buffer_mask)) {
@@ -3103,14 +3093,6 @@ static ssize_t tracing_resize_ring_buffer(unsigned long size, int cpu_id)
 		ret = -ENOMEM;
 
 out:
-	for_each_tracing_cpu(cpu) {
-		if (global_trace.data[cpu])
-			atomic_dec(&global_trace.data[cpu]->disabled);
-		if (max_tr.data[cpu])
-			atomic_dec(&max_tr.data[cpu]->disabled);
-	}
-
-	tracing_start();
 	mutex_unlock(&trace_types_lock);
 
 	return ret;