ring-buffer: Move access to commit_page up into function used

With the change of the way we process commits. Where a commit only happens
at the outer most level, and that we don't need to worry about
a commit ending after the rb_start_commit() has been called, the code
use to grab the commit page before the tail page to prevent a possible
race. But this race no longer exists with the rb_start_commit()
rb_end_commit() interface.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 3ffa502fb243..4b8293fa545e 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1785,9 +1785,9 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
 static struct ring_buffer_event *
 rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
              unsigned long length, unsigned long tail,
-             struct buffer_page *commit_page,
              struct buffer_page *tail_page, u64 *ts)
 {
+        struct buffer_page *commit_page = cpu_buffer->commit_page;
         struct ring_buffer *buffer = cpu_buffer->buffer;
         struct buffer_page *next_page;
         int ret;
@@ -1890,13 +1890,10 @@ static struct ring_buffer_event *
 __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
                   unsigned type, unsigned long length, u64 *ts)
 {
-        struct buffer_page *tail_page, *commit_page;
+        struct buffer_page *tail_page;
         struct ring_buffer_event *event;
         unsigned long tail, write;
 
-        commit_page = cpu_buffer->commit_page;
-        /* we just need to protect against interrupts */
-        barrier();
         tail_page = cpu_buffer->tail_page;
         write = local_add_return(length, &tail_page->write);
 
@@ -1907,7 +1904,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
         /* See if we shot pass the end of this buffer page */
         if (write > BUF_PAGE_SIZE)
                 return rb_move_tail(cpu_buffer, length, tail,
-                                    commit_page, tail_page, ts);
+                                    tail_page, ts);
 
         /* We reserved something on the buffer */