On Thu, 28 May 2026 22:37:38 -0400 Steven Rostedt <[email protected]> wrote:
> From: Steven Rostedt <[email protected]> > > If the persistent ring buffer is detected on boot up to have a corrupted > sub-buffer, that sub-buffer is cleared to zero and its commit value has > the RB_MISSED_EVENTS bit set. That bit is to allow the "trace", > "trace_pipe" and "trace_pipe_raw" files know that events were dropped by > outputting "[LOST EVENTS]". > > Only in this case does that bit get set in the writeable portion of the > ring buffer. When events are dropped in the normal ring buffer, that > information is stored in the cpu_buffer descriptor and the > RB_MISSED_EVENTS is set in the buffer page at the time the page is > consumed. It is never set in the writeable portion of the buffer. > > Add comments to describe this better as it can be confusing to know when > the RB_MISSED_EVENTS are set in the commit portion of the buffer page. > > Link: > https://lore.kernel.org/all/[email protected]/ > This looks good to me. Acked-by: Masami Hiramatsu (Google) <[email protected]> Thanks, > Signed-off-by: Steven Rostedt <[email protected]> > --- > kernel/trace/ring_buffer.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 910f6b3adf74..06fb365bb86e 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); > } > > -- > 2.53.0 > -- Masami Hiramatsu (Google) <[email protected]>
