1 files changed, 52 insertions, 13 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b979426d16c6..ce8514feedcd 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -460,9 +460,10 @@ struct ring_buffer_per_cpu {
         unsigned long                   lost_events;
         unsigned long                   last_overrun;
         local_t                         entries_bytes;
-        local_t                         commit_overrun;
-        local_t                         overrun;
         local_t                         entries;
+        local_t                         overrun;
+        local_t                         commit_overrun;
+        local_t                         dropped_events;
         local_t                         committing;
         local_t                         commits;
         unsigned long                   read;
@@ -1396,6 +1397,8 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
                 struct list_head *head_page_with_bit;
 
                 head_page = &rb_set_head_page(cpu_buffer)->list;
+                if (!head_page)
+                        break;
                 prev_page = head_page->prev;
 
                 first_page = pages->next;
@@ -1820,7 +1823,7 @@ rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
 }
 
 /**
- * ring_buffer_update_event - update event type and data
+ * rb_update_event - update event type and data
  * @event: the even to update
  * @type: the type of event
  * @length: the size of the event field in the ring buffer
@@ -2155,8 +2158,10 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
                          * If we are not in overwrite mode,
                          * this is easy, just stop here.
                          */
-                        if (!(buffer->flags & RB_FL_OVERWRITE))
+                        if (!(buffer->flags & RB_FL_OVERWRITE)) {
+                                local_inc(&cpu_buffer->dropped_events);
                                 goto out_reset;
+                        }
 
                         ret = rb_handle_head_page(cpu_buffer,
                                                   tail_page,
@@ -2720,8 +2725,8 @@ EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
  * and not the length of the event which would hold the header.
  */
 int ring_buffer_write(struct ring_buffer *buffer,
-                        unsigned long length,
-                        void *data)
+                      unsigned long length,
+                      void *data)
 {
         struct ring_buffer_per_cpu *cpu_buffer;
         struct ring_buffer_event *event;
@@ -2929,12 +2934,12 @@ rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
  * @buffer: The ring buffer
  * @cpu: The per CPU buffer to read from.
  */
-unsigned long ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
+u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
 {
         unsigned long flags;
         struct ring_buffer_per_cpu *cpu_buffer;
         struct buffer_page *bpage;
-        unsigned long ret;
+        u64 ret = 0;
 
         if (!cpumask_test_cpu(cpu, buffer->cpumask))
                 return 0;
@@ -2949,7 +2954,8 @@ unsigned long ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
                 bpage = cpu_buffer->reader_page;
         else
                 bpage = rb_set_head_page(cpu_buffer);
-        ret = bpage->page->time_stamp;
+        if (bpage)
+                ret = bpage->page->time_stamp;
         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
         return ret;
@@ -2995,7 +3001,8 @@ unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
 EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
 
 /**
- * ring_buffer_overrun_cpu - get the number of overruns in a cpu_buffer
+ * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
+ * buffer wrapping around (only if RB_FL_OVERWRITE is on).
  * @buffer: The ring buffer
  * @cpu: The per CPU buffer to get the number of overruns from
  */
@@ -3015,7 +3022,9 @@ unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
 EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
 
 /**
- * ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits
+ * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
+ * commits failing due to the buffer wrapping around while there are uncommitted
+ * events, such as during an interrupt storm.
  * @buffer: The ring buffer
  * @cpu: The per CPU buffer to get the number of overruns from
  */
@@ -3036,6 +3045,28 @@ ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
 EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
 
 /**
+ * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
+ * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to get the number of overruns from
+ */
+unsigned long
+ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
+{
+        struct ring_buffer_per_cpu *cpu_buffer;
+        unsigned long ret;
+
+        if (!cpumask_test_cpu(cpu, buffer->cpumask))
+                return 0;
+
+        cpu_buffer = buffer->buffers[cpu];
+        ret = local_read(&cpu_buffer->dropped_events);
+
+        return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
+
+/**
  * ring_buffer_entries - get the number of entries in a buffer
  * @buffer: The ring buffer
  *
@@ -3260,6 +3291,8 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
          * Splice the empty reader page into the list around the head.
          */
         reader = rb_set_head_page(cpu_buffer);
+        if (!reader)
+                goto out;
         cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
         cpu_buffer->reader_page->list.prev = reader->list.prev;
 
@@ -3778,12 +3811,17 @@ void
 ring_buffer_read_finish(struct ring_buffer_iter *iter)
 {
         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
+        unsigned long flags;
 
         /*
          * Ring buffer is disabled from recording, here's a good place
-         * to check the integrity of the ring buffer. 
+         * to check the integrity of the ring buffer.
+         * Must prevent readers from trying to read, as the check
+         * clears the HEAD page and readers require it.
          */
+        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
         rb_check_pages(cpu_buffer);
+        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
         atomic_dec(&cpu_buffer->record_disabled);
         atomic_dec(&cpu_buffer->buffer->resize_disabled);
@@ -3864,9 +3902,10 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
         local_set(&cpu_buffer->reader_page->page->commit, 0);
         cpu_buffer->reader_page->read = 0;
 
-        local_set(&cpu_buffer->commit_overrun, 0);
         local_set(&cpu_buffer->entries_bytes, 0);
         local_set(&cpu_buffer->overrun, 0);
+        local_set(&cpu_buffer->commit_overrun, 0);
+        local_set(&cpu_buffer->dropped_events, 0);
         local_set(&cpu_buffer->entries, 0);
         local_set(&cpu_buffer->committing, 0);
         local_set(&cpu_buffer->commits, 0);