Commit b3230c8b authored May 21, 2010 by Steven Rostedt Committed by Steven Rostedt May 25, 2010

ring-buffer: Reset "real_end" when page is filled



The code to store the "lost events" requires knowing the real end
of the page. Since the 'commit' includes the padding at the end of
a page a "real_end" variable was used to keep track of the end not
including the padding.

If events were lost, the reader can place the count of events in
the padded area if there is enough room.

The bug this patch fixes is that when we fill the page we do not
reset the real_end variable, and if the writer had wrapped a few
times, the real_end would be incorrect.

This patch simply resets the real_end if the page was filled.

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

parent 49c17746

kernel/trace/ring_buffer.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -1768,6 +1768,14 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
		* must fill the old tail_page with padding.
		*/
		if (tail >= BUF_PAGE_SIZE) {
		/*
		* If the page was filled, then we still need
		* to update the real_end. Reset it to zero
		* and the reader will ignore it.
		*/
		if (tail == BUF_PAGE_SIZE)
		tail_page->real_end = 0;

		local_sub(length, &tail_page->write);
		return;
		}