ring_buffer: fix ring_buffer_read_page()

Impact: change API and init bpage when copy

ring_buffer_read_page()/rb_remove_entries() may be called for
a partially consumed page.

Add a parameter for rb_remove_entries() and make it update
cpu_buffer->entries correctly for partially consumed pages.

ring_buffer_read_page() now returns the offset to the next event.

Init the bpage's time_stamp when return value is 0.

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

1 files changed, 20 insertions, 13 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index eca282720838..10d202ea06f3 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2332,13 +2332,14 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
 
 static void rb_remove_entries(struct ring_buffer_per_cpu *cpu_buffer,
-                              struct buffer_data_page *bpage)
+                              struct buffer_data_page *bpage,
+                              unsigned int offset)
 {
         struct ring_buffer_event *event;
         unsigned long head;
 
         __raw_spin_lock(&cpu_buffer->lock);
-        for (head = 0; head < local_read(&bpage->commit);
+        for (head = offset; head < local_read(&bpage->commit);
              head += rb_event_length(event)) {
 
                 event = __rb_data_page_index(bpage, head);
@@ -2410,8 +2411,8 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
  *      if (!rpage)
  *              return error;
  *      ret = ring_buffer_read_page(buffer, &rpage, cpu, 0);
- *      if (ret)
- *              process_page(rpage);
+ *      if (ret >= 0)
+ *              process_page(rpage, ret);
  *
  * When @full is set, the function will not return true unless
  * the writer is off the reader page.
@@ -2422,8 +2423,8 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
  *  responsible for that.
  *
  * Returns:
- *  1 if data has been transferred
- *  0 if no data has been transferred.
+ *  >=0 if data has been transferred, returns the offset of consumed data.
+ *  <0 if no data has been transferred.
  */
 int ring_buffer_read_page(struct ring_buffer *buffer,
                             void **data_page, int cpu, int full)
@@ -2432,7 +2433,8 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
         struct ring_buffer_event *event;
         struct buffer_data_page *bpage;
         unsigned long flags;
-        int ret = 0;
+        unsigned int read;
+        int ret = -1;
 
         if (!data_page)
                 return 0;
@@ -2454,24 +2456,29 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
         /* check for data */
         if (!local_read(&cpu_buffer->reader_page->page->commit))
                 goto out;
+
+        read = cpu_buffer->reader_page->read;
         /*
          * If the writer is already off of the read page, then simply
          * switch the read page with the given page. Otherwise
          * we need to copy the data from the reader to the writer.
          */
         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);
+                struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
 
                 if (full)
                         goto out;
                 /* The writer is still on the reader page, we must copy */
-                memcpy(bpage->data,
-                       cpu_buffer->reader_page->page->data + read,
-                       commit - read);
+                memcpy(bpage->data + read, rpage->data + read, commit - read);
 
                 /* consume what was read */
                 cpu_buffer->reader_page->read = commit;
+
+                /* update bpage */
+                local_set(&bpage->commit, commit);
+                if (!read)
+                        bpage->time_stamp = rpage->time_stamp;
         } else {
                 /* swap the pages */
                 rb_init_page(bpage);
@@ -2480,10 +2487,10 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
                 cpu_buffer->reader_page->read = 0;
                 *data_page = bpage;
         }
-        ret = 1;
+        ret = read;
 
         /* update the entry counter */
-        rb_remove_entries(cpu_buffer, bpage);
+        rb_remove_entries(cpu_buffer, bpage, read);
  out:
         spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);