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authorSteven Rostedt <srostedt@redhat.com>2010-05-21 11:55:21 -0400
committerSteven Rostedt <rostedt@goodmis.org>2010-05-25 11:57:24 -0400
commitb3230c8b44da5838cf396942d5c1ab19f8e8f720 (patch)
tree21a212bb598da40cdb936f7b4492d9b05895d4fc /kernel
parent49c177461bfbedeccbab22bf3905db2f9da7f1c3 (diff)
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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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/ring_buffer.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 7f6059c5aa9..b0702ff7821 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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;
}