ring-buffer: move big if statement down

In the hot path of the ring buffer "__rb_reserve_next" there's a big
if statement that does not even return back to the work flow.

	code;

	if (cross to next page) {

		[ lots of code ]

		return;
	}

	more code;

The condition is even the unlikely path, although we do not denote it
with an unlikely because gcc is fine with it. The condition is true when
the write crosses a page boundary, and we need to start at a new page.

Having this if statement makes it hard to read, but calling another
function to do the work is also not appropriate, because we are using a lot
of variables that were set before the if statement, and we do not want to
send them as parameters.

This patch changes it to a goto:

	code;

	if (cross to next page)
		goto next_page;

	more code;

	return;

next_page:

	[ lots of code]

This makes the code easier to understand, and a bit more obvious.

The output from gcc is practically identical. For some reason, gcc decided
to use different registers when I switched it to a goto. But other than that,
the logic is the same.

[ Impact: easier to read code ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ring_buffer.c

@@ -1159,6 +1159,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		  unsigned type, unsigned long length, u64 *ts)
 {
 	struct buffer_page *tail_page, *head_page, *reader_page, *commit_page;
+	struct buffer_page *next_page;
 	unsigned long tail, write;
 	struct ring_buffer *buffer = cpu_buffer->buffer;
 	struct ring_buffer_event *event;
@@ -1173,8 +1174,33 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	tail = write - length;
 
 	/* See if we shot pass the end of this buffer page */
-	if (write > BUF_PAGE_SIZE) {
-		struct buffer_page *next_page = tail_page;
+	if (write > BUF_PAGE_SIZE)
+		goto next_page;
+
+	/* We reserved something on the buffer */
+
+	if (RB_WARN_ON(cpu_buffer, write > BUF_PAGE_SIZE))
+		return NULL;
+
+	event = __rb_page_index(tail_page, tail);
+	rb_update_event(event, type, length);
+
+	/* The passed in type is zero for DATA */
+	if (likely(!type))
+		local_inc(&tail_page->entries);
+
+	/*
+	 * If this is a commit and the tail is zero, then update
+	 * this page's time stamp.
+	 */
+	if (!tail && rb_is_commit(cpu_buffer, event))
+		cpu_buffer->commit_page->page->time_stamp = *ts;
+
+	return event;
+
+ next_page:
+
+	next_page = tail_page;
 
 	local_irq_save(flags);
 	/*
@@ -1282,28 +1308,6 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 
 	/* fail and let the caller try again */
 	return ERR_PTR(-EAGAIN);
-	}
-
-	/* We reserved something on the buffer */
-
-	if (RB_WARN_ON(cpu_buffer, write > BUF_PAGE_SIZE))
-		return NULL;
-
-	event = __rb_page_index(tail_page, tail);
-	rb_update_event(event, type, length);
-
-	/* The passed in type is zero for DATA */
-	if (likely(!type))
-		local_inc(&tail_page->entries);
-
-	/*
-	 * If this is a commit and the tail is zero, then update
-	 * this page's time stamp.
-	 */
-	if (!tail && rb_is_commit(cpu_buffer, event))
-		cpu_buffer->commit_page->page->time_stamp = *ts;
-
-	return event;
 
  out_reset:
 	/* reset write */