1 files changed, 21 insertions, 16 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 50926601a28d..7102d7a2fadb 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -370,6 +370,9 @@ static inline int test_time_stamp(u64 delta)
 /* Max payload is BUF_PAGE_SIZE - header (8bytes) */
 #define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
 
+/* Max number of timestamps that can fit on a page */
+#define RB_TIMESTAMPS_PER_PAGE  (BUF_PAGE_SIZE / RB_LEN_TIME_STAMP)
+
 int ring_buffer_print_page_header(struct trace_seq *s)
 {
         struct buffer_data_page field;
@@ -1409,8 +1412,12 @@ rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
                         event->array[0] = *delta >> TS_SHIFT;
                 } else {
                         cpu_buffer->commit_page->page->time_stamp = *ts;
-                        event->time_delta = 0;
-                        event->array[0] = 0;
+                        /* try to discard, since we do not need this */
+                        if (!rb_try_to_discard(cpu_buffer, event)) {
+                                /* nope, just zero it */
+                                event->time_delta = 0;
+                                event->array[0] = 0;
+                        }
                 }
                 cpu_buffer->write_stamp = *ts;
                 /* let the caller know this was the commit */
@@ -2268,8 +2275,8 @@ static void rb_advance_iter(struct ring_buffer_iter *iter)
          * Check if we are at the end of the buffer.
          */
         if (iter->head >= rb_page_size(iter->head_page)) {
-                if (RB_WARN_ON(buffer,
-                               iter->head_page == cpu_buffer->commit_page))
+                /* discarded commits can make the page empty */
+                if (iter->head_page == cpu_buffer->commit_page)
                         return;
                 rb_inc_iter(iter);
                 return;
@@ -2312,12 +2319,10 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
         /*
          * We repeat when a timestamp is encountered. It is possible
          * to get multiple timestamps from an interrupt entering just
-         * as one timestamp is about to be written. The max times
-         * that this can happen is the number of nested interrupts we
-         * can have.  Nesting 10 deep of interrupts is clearly
-         * an anomaly.
+         * as one timestamp is about to be written, or from discarded
+         * commits. The most that we can have is the number on a single page.
          */
-        if (RB_WARN_ON(cpu_buffer, ++nr_loops > 10))
+        if (RB_WARN_ON(cpu_buffer, ++nr_loops > RB_TIMESTAMPS_PER_PAGE))
                 return NULL;
 
         reader = rb_get_reader_page(cpu_buffer);
@@ -2383,14 +2388,14 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 
  again:
         /*
-         * We repeat when a timestamp is encountered. It is possible
-         * to get multiple timestamps from an interrupt entering just
-         * as one timestamp is about to be written. The max times
-         * that this can happen is the number of nested interrupts we
-         * can have. Nesting 10 deep of interrupts is clearly
-         * an anomaly.
+         * We repeat when a timestamp is encountered.
+         * We can get multiple timestamps by nested interrupts or also
+         * if filtering is on (discarding commits). Since discarding
+         * commits can be frequent we can get a lot of timestamps.
+         * But we limit them by not adding timestamps if they begin
+         * at the start of a page.
          */
-        if (RB_WARN_ON(cpu_buffer, ++nr_loops > 10))
+        if (RB_WARN_ON(cpu_buffer, ++nr_loops > RB_TIMESTAMPS_PER_PAGE))
                 return NULL;
 
         if (rb_per_cpu_empty(cpu_buffer))