trace: annotate bitfields in struct ring_buffer_event

This gets rid of a heap of false-positive warnings from the tracer
code due to the use of bitfields.

[rebased for mainline inclusion]
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>

kernel/trace/ring_buffer.c

@@ -10,6 +10,7 @@
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
 #include <linux/hardirq.h>
+#include <linux/kmemcheck.h>
 #include <linux/module.h>
 #include <linux/percpu.h>
 #include <linux/mutex.h>
@@ -1270,6 +1271,7 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
 	if (tail < BUF_PAGE_SIZE) {
 		/* Mark the rest of the page with padding */
 		event = __rb_page_index(tail_page, tail);
+		kmemcheck_annotate_bitfield(event, bitfield);
 		rb_event_set_padding(event);
 	}
 
@@ -1327,6 +1329,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		return NULL;
 
 	event = __rb_page_index(tail_page, tail);
+	kmemcheck_annotate_bitfield(event, bitfield);
 	rb_update_event(event, type, length);
 
 	/* The passed in type is zero for DATA */