Merge branch 'tip/perf/urgent-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace into perf/urgent

Pull ftrace fixes from Steve Rostedt.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 13 insertions, 3 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b979426d16c6..4cb5e5147165 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1396,6 +1396,8 @@ 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;
@@ -2934,7 +2936,7 @@ unsigned long 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;
+        unsigned long ret = 0;
 
         if (!cpumask_test_cpu(cpu, buffer->cpumask))
                 return 0;
@@ -2949,7 +2951,8 @@ 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;
@@ -3260,6 +3263,8 @@ 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 +3783,17 @@ 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);