ring-buffer: Fix ring_buffer_read_page() copying only one event per page

Commit 8928e4a3be34 ("ring-buffer: Show persistent buffer dropped events
in trace_pipe file") split the "commit" variable in
ring_buffer_read_page() into "commit" (raw) and "size" (masked page
size), but the inner copy loop's terminator was changed to compare rpos
against "event_size" instead of "size".

rpos is the cumulative read offset within the page; event_size is the
length of the single event just copied. The loop thus breaks after the
first event, so only one event is copied per call. This regresses the
per-event memcpy path (partial reads, the active commit page, and
mapped/remote buffers) used by splice/trace_pipe_raw and mmap consumers
into a one-event-at-a-time read.

Compare rpos against the page size as the original code did.

Link: https://patch.msgid.link/20260616175538.111628-1-devnexen@gmail.com
Fixes: 8928e4a3be34 ("ring-buffer: Show persistent buffer dropped events in trace_pipe file")
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index d9af2bbaf9c08108644d540030f7bb9cf87b242c..12a83d9ffd0a94d0150084a1c5b0ee402fbded05 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -7175,7 +7175,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
                        rpos = reader->read;
                        pos += event_size;
 
-                       if (rpos >= event_size)
+                       if (rpos >= size)
                                break;
 
                        event = rb_reader_event(cpu_buffer);