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>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 3ffa502..4b8293f 100644 (file)
--- 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 */