tracing: add ring_buffer_event_discard() to ring buffer
This patch overloads RINGBUF_TYPE_PADDING to provide a way to discard
events from the ring buffer, for the event-filtering mechanism
introduced in a subsequent patch.
I did the initial version but thanks to Steven Rostedt for adding
the parts that actually made it work. ;-)
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 9e6052b..e1b7b21 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -18,10 +18,13 @@
/**
* enum ring_buffer_type - internal ring buffer types
*
- * @RINGBUF_TYPE_PADDING: Left over page padding
- * array is ignored
- * size is variable depending on how much
+ * @RINGBUF_TYPE_PADDING: Left over page padding or discarded event
+ * If time_delta is 0:
+ * array is ignored
+ * size is variable depending on how much
* padding is needed
+ * If time_delta is non zero:
+ * everything else same as RINGBUF_TYPE_DATA
*
* @RINGBUF_TYPE_TIME_EXTEND: Extend the time delta
* array[0] = time delta (28 .. 59)
@@ -65,6 +68,8 @@
return event->time_delta;
}
+void ring_buffer_event_discard(struct ring_buffer_event *event);
+
/*
* size is in bytes for each per CPU buffer.
*/
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 384ca5d..a09027e 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -189,16 +189,65 @@
RB_LEN_TIME_STAMP = 16,
};
+static inline int rb_null_event(struct ring_buffer_event *event)
+{
+ return event->type == RINGBUF_TYPE_PADDING && event->time_delta == 0;
+}
+
+static inline int rb_discarded_event(struct ring_buffer_event *event)
+{
+ return event->type == RINGBUF_TYPE_PADDING && event->time_delta;
+}
+
+static void rb_event_set_padding(struct ring_buffer_event *event)
+{
+ event->type = RINGBUF_TYPE_PADDING;
+ event->time_delta = 0;
+}
+
+/**
+ * ring_buffer_event_discard - discard an event in the ring buffer
+ * @buffer: the ring buffer
+ * @event: the event to discard
+ *
+ * Sometimes a event that is in the ring buffer needs to be ignored.
+ * This function lets the user discard an event in the ring buffer
+ * and then that event will not be read later.
+ *
+ * Note, it is up to the user to be careful with this, and protect
+ * against races. If the user discards an event that has been consumed
+ * it is possible that it could corrupt the ring buffer.
+ */
+void ring_buffer_event_discard(struct ring_buffer_event *event)
+{
+ event->type = RINGBUF_TYPE_PADDING;
+ /* time delta must be non zero */
+ if (!event->time_delta)
+ event->time_delta = 1;
+}
+
+static unsigned
+rb_event_data_length(struct ring_buffer_event *event)
+{
+ unsigned length;
+
+ if (event->len)
+ length = event->len * RB_ALIGNMENT;
+ else
+ length = event->array[0];
+ return length + RB_EVNT_HDR_SIZE;
+}
+
/* inline for ring buffer fast paths */
static unsigned
rb_event_length(struct ring_buffer_event *event)
{
- unsigned length;
-
switch (event->type) {
case RINGBUF_TYPE_PADDING:
- /* undefined */
- return -1;
+ if (rb_null_event(event))
+ /* undefined */
+ return -1;
+ return rb_event_data_length(event);
case RINGBUF_TYPE_TIME_EXTEND:
return RB_LEN_TIME_EXTEND;
@@ -207,11 +256,7 @@
return RB_LEN_TIME_STAMP;
case RINGBUF_TYPE_DATA:
- if (event->len)
- length = event->len * RB_ALIGNMENT;
- else
- length = event->array[0];
- return length + RB_EVNT_HDR_SIZE;
+ return rb_event_data_length(event);
default:
BUG();
}
@@ -845,11 +890,6 @@
}
EXPORT_SYMBOL_GPL(ring_buffer_resize);
-static inline int rb_null_event(struct ring_buffer_event *event)
-{
- return event->type == RINGBUF_TYPE_PADDING;
-}
-
static inline void *
__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
{
@@ -1219,7 +1259,7 @@
if (tail < BUF_PAGE_SIZE) {
/* Mark the rest of the page with padding */
event = __rb_page_index(tail_page, tail);
- event->type = RINGBUF_TYPE_PADDING;
+ rb_event_set_padding(event);
}
if (tail <= BUF_PAGE_SIZE)
@@ -1969,7 +2009,7 @@
event = rb_reader_event(cpu_buffer);
- if (event->type == RINGBUF_TYPE_DATA)
+ if (event->type == RINGBUF_TYPE_DATA || rb_discarded_event(event))
cpu_buffer->entries--;
rb_update_read_stamp(cpu_buffer, event);
@@ -2052,9 +2092,18 @@
switch (event->type) {
case RINGBUF_TYPE_PADDING:
- RB_WARN_ON(cpu_buffer, 1);
+ if (rb_null_event(event))
+ RB_WARN_ON(cpu_buffer, 1);
+ /*
+ * Because the writer could be discarding every
+ * event it creates (which would probably be bad)
+ * if we were to go back to "again" then we may never
+ * catch up, and will trigger the warn on, or lock
+ * the box. Return the padding, and we will release
+ * the current locks, and try again.
+ */
rb_advance_reader(cpu_buffer);
- return NULL;
+ return event;
case RINGBUF_TYPE_TIME_EXTEND:
/* Internal data, OK to advance */
@@ -2115,8 +2164,12 @@
switch (event->type) {
case RINGBUF_TYPE_PADDING:
- rb_inc_iter(iter);
- goto again;
+ if (rb_null_event(event)) {
+ rb_inc_iter(iter);
+ goto again;
+ }
+ rb_advance_iter(iter);
+ return event;
case RINGBUF_TYPE_TIME_EXTEND:
/* Internal data, OK to advance */
@@ -2163,10 +2216,16 @@
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return NULL;
+ again:
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_buffer_peek(buffer, cpu, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+ if (event && event->type == RINGBUF_TYPE_PADDING) {
+ cpu_relax();
+ goto again;
+ }
+
return event;
}
@@ -2185,10 +2244,16 @@
struct ring_buffer_event *event;
unsigned long flags;
+ again:
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_iter_peek(iter, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+ if (event && event->type == RINGBUF_TYPE_PADDING) {
+ cpu_relax();
+ goto again;
+ }
+
return event;
}
@@ -2207,6 +2272,7 @@
struct ring_buffer_event *event = NULL;
unsigned long flags;
+ again:
/* might be called in atomic */
preempt_disable();
@@ -2228,6 +2294,11 @@
out:
preempt_enable();
+ if (event && event->type == RINGBUF_TYPE_PADDING) {
+ cpu_relax();
+ goto again;
+ }
+
return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_consume);
@@ -2306,6 +2377,7 @@
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
unsigned long flags;
+ again:
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_iter_peek(iter, ts);
if (!event)
@@ -2315,6 +2387,11 @@
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+ if (event && event->type == RINGBUF_TYPE_PADDING) {
+ cpu_relax();
+ goto again;
+ }
+
return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_read);