On Fri, 29 May 2026 00:15:00 +0900
Masami Hiramatsu (Google) <[email protected]> wrote:
> Yeah, the relationship between the persistent ring buffer (which is mapped)
> and the RB_MISSED_EVENTS is a bit unclear.
I'm going to pull these patches into the ring-buffer for-next branch and
start testing it. If they pass, I'll push them up to the linux-trace repo.
I'll send out this patch on top of it.
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 910f6b3adf74..5de6f352249a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1929,6 +1929,12 @@ static int __rb_validate_buffer(struct buffer_page
*bpage, int cpu,
*/
if (ret < 0 || (prev_ts && prev_ts > ts) || (next_ts && ts > next_ts)) {
local_set(&bpage->entries, 0);
+ /*
+ * Note, the RB_MISSED_EVENTS is only set inside the main write
+ * buffer by this verification logic. The normal ring buffer
+ * has this bit set when the page is read and passed to the
+ * consumers.
+ */
local_set(&dpage->commit, RB_MISSED_EVENTS);
dpage->time_stamp = prev_ts ? prev_ts : next_ts;
ret = -1;
@@ -7232,6 +7238,14 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
local_add(RB_MISSED_STORED, &dpage->commit);
size += sizeof(missed_events);
}
+ /*
+ * Note, for the persistent ring buffer, the RB_MISSED_EVENTS
+ * may have been set in the main buffer via the verification
code.
+ * But here, dpage is a copy of that page and has not yet had
+ * the RB_MISSED_EVENTS set. As for the normal buffers,
+ * the main write buffer does not set these bits and it needs
+ * to be set here.
+ */
local_add(RB_MISSED_EVENTS, &dpage->commit);
}
-- Steve
