ring_buffer: fix typing mistake

Impact: Fix bug

I found several very very curious line.
It's so curious that it may be brought by typing mistake.

When (cpu_buffer->reader_page == cpu_buffer->commit_page):

1) We haven't copied it for bpage is changed:
   bpage = cpu_buffer->reader_page->page;
   memcpy(bpage->data, cpu_buffer->reader_page->page->data + read ... )
2) We need update cpu_buffer->reader_page->read, but
   "cpu_buffer->reader_page += read;" is not right.

[
  This bug was a typo. The commit->reader_page is a page pointer
  and not an index into the page. The line should have been
  commit->reader_page->read += read.  The other changes
  by Lai are nice clean ups to the code.  - SDR
]

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 53ba3a6d16d0..eca282720838 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2406,7 +2406,7 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
  * to swap with a page in the ring buffer.
  *
  * for example:
- *      rpage = ring_buffer_alloc_page(buffer);
+ *      rpage = ring_buffer_alloc_read_page(buffer);
  *      if (!rpage)
  *              return error;
  *      ret = ring_buffer_read_page(buffer, &rpage, cpu, 0);
@@ -2461,18 +2461,17 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
          */
         if (cpu_buffer->reader_page == cpu_buffer->commit_page) {
                 unsigned int read = cpu_buffer->reader_page->read;
+                unsigned int commit = rb_page_commit(cpu_buffer->reader_page);
 
                 if (full)
                         goto out;
                 /* The writer is still on the reader page, we must copy */
-                bpage = cpu_buffer->reader_page->page;
                 memcpy(bpage->data,
                        cpu_buffer->reader_page->page->data + read,
-                       local_read(&bpage->commit) - read);
+                       commit - read);
 
                 /* consume what was read */
-                cpu_buffer->reader_page += read;
-
+                cpu_buffer->reader_page->read = commit;
         } else {
                 /* swap the pages */
                 rb_init_page(bpage);