1 files changed, 62 insertions, 42 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 16b24d49604c..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;
@@ -1335,6 +1338,38 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
         return event;
 }
 
+static inline int
+rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
+                  struct ring_buffer_event *event)
+{
+        unsigned long new_index, old_index;
+        struct buffer_page *bpage;
+        unsigned long index;
+        unsigned long addr;
+
+        new_index = rb_event_index(event);
+        old_index = new_index + rb_event_length(event);
+        addr = (unsigned long)event;
+        addr &= PAGE_MASK;
+
+        bpage = cpu_buffer->tail_page;
+
+        if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
+                /*
+                 * This is on the tail page. It is possible that
+                 * a write could come in and move the tail page
+                 * and write to the next page. That is fine
+                 * because we just shorten what is on this page.
+                 */
+                index = local_cmpxchg(&bpage->write, old_index, new_index);
+                if (index == old_index)
+                        return 1;
+        }
+
+        /* could not discard */
+        return 0;
+}
+
 static int
 rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
                   u64 *ts, u64 *delta)
@@ -1377,17 +1412,24 @@ 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 */
                 ret = 1;
         } else {
-                /* Darn, this is just wasted space */
-                event->time_delta = 0;
-                event->array[0] = 0;
-                ret = 0;
+                /* Try to discard the event */
+                if (!rb_try_to_discard(cpu_buffer, event)) {
+                        /* Darn, this is just wasted space */
+                        event->time_delta = 0;
+                        event->array[0] = 0;
+                        ret = 0;
+                }
         }
 
         *delta = 0;
@@ -1682,10 +1724,6 @@ void ring_buffer_discard_commit(struct ring_buffer *buffer,
                                 struct ring_buffer_event *event)
 {
         struct ring_buffer_per_cpu *cpu_buffer;
-        unsigned long new_index, old_index;
-        struct buffer_page *bpage;
-        unsigned long index;
-        unsigned long addr;
         int cpu;
 
         /* The event is discarded regardless */
@@ -1701,24 +1739,8 @@ void ring_buffer_discard_commit(struct ring_buffer *buffer,
         cpu = smp_processor_id();
         cpu_buffer = buffer->buffers[cpu];
 
-        new_index = rb_event_index(event);
-        old_index = new_index + rb_event_length(event);
-        addr = (unsigned long)event;
-        addr &= PAGE_MASK;
-
-        bpage = cpu_buffer->tail_page;
-
-        if (bpage == (void *)addr && rb_page_write(bpage) == old_index) {
-                /*
-                 * This is on the tail page. It is possible that
-                 * a write could come in and move the tail page
-                 * and write to the next page. That is fine
-                 * because we just shorten what is on this page.
-                 */
-                index = local_cmpxchg(&bpage->write, old_index, new_index);
-                if (index == old_index)
-                        goto out;
-        }
+        if (!rb_try_to_discard(cpu_buffer, event))
+                goto out;
 
         /*
          * The commit is still visible by the reader, so we
@@ -2253,8 +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;
@@ -2297,12 +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);
@@ -2368,14 +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))