From c37e0a4b79a6bbb96ce5ffe279d7c001e20529e0 Mon Sep 17 00:00:00 2001 From: Hui Wang Date: Sun, 7 Jun 2026 15:24:30 +0800 Subject: ring-buffer: Fix event length with forced 8-byte alignment When RB_FORCE_8BYTE_ALIGNMENT is true, rb_calculate_event_length() reserves the space of event->array[0] for placing the data length and rb_update_event() stores the data length in event->array[0] accordingly. As a result the whole event length will add extra 4 bytes for sizeof(event.array[0]) unconditionally. But ring_buffer_event_length() only subtracts the sizeof(event->array[0]) for events larger than RB_MAX_SMALL_DATA + sizeof(event->array[0]). As a result, small events on architectures with RB_FORCE_8BYTE_ALIGNMENT=true report a data length that is 4 bytes larger than expected. To fix it, add the RB_FORCE_8BYTE_ALIGNMENT as a condition to subtract the size of that length field whenever RB_FORCE_8BYTE_ALIGNMENT is true. This issue is observed in a riscv64 kernel with CONFIG_HAVE_64BIT_ALIGNED_ACCESS set to y, when we run ftrace selftest trace_marker_raw.tc, we get the weird log: for cases where the id is 1..100, the number of data field is 8*N, but once id exceeds 100, the number of data field becomes 8*N+4: # 1 buf: 58 00 00 00 80 5e d1 63 (number of data field is 8*1) ... # a buf: 58 ... (number of data field is 8*2) ... # 64 buf: 58 ... (number of data field is 8*13) # 65 buf: 58 ... (number of data field is 8*13+4) After applying this change, the number of data field keeps being 8*N+4 consistently. Link: https://patch.msgid.link/20260607072431.125633-2-hui.wang@canonical.com Fixes: 2271048d1b3b ("ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align") Signed-off-by: Hui Wang Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/trace/ring_buffer.c') diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 56a328e94395..d9af2bbaf9c0 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -270,7 +270,8 @@ unsigned ring_buffer_event_length(struct ring_buffer_event *event) if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX) return length; length -= RB_EVNT_HDR_SIZE; - if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0])) + if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]) || + RB_FORCE_8BYTE_ALIGNMENT) length -= sizeof(event->array[0]); return length; } -- cgit v1.2.3 From af05b4e06279bbe34f8044b1e82f0725b5da91b7 Mon Sep 17 00:00:00 2001 From: David Carlier Date: Tue, 16 Jun 2026 18:55:38 +0100 Subject: 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 Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/trace/ring_buffer.c') diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index d9af2bbaf9c0..12a83d9ffd0a 100644 --- 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); -- cgit v1.2.3 From 601ddaceb861be7eb557278109966320a6f3478c Mon Sep 17 00:00:00 2001 From: Vincent Donnefort Date: Thu, 9 Jul 2026 17:00:17 +0100 Subject: ring-buffer: Allow sparse CPU masks in ring_buffer_desc() No user currently relies on sparse CPU masks, but the descriptor logic already supports them via linear fallback. Remove the arbitrary limitation. Link: https://patch.msgid.link/20260709160017.1729517-4-vdonnefort@google.com Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes") Reported-by: Sashiko Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'kernel/trace/ring_buffer.c') diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 12a83d9ffd0a..804ccae694d2 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2330,10 +2330,7 @@ static struct ring_buffer_desc *ring_buffer_desc(struct trace_buffer_desc *trace size_t len; int i; - if (!trace_desc) - return NULL; - - if (cpu >= trace_desc->nr_cpus) + if (!trace_desc || !trace_desc->nr_cpus) return NULL; end = (struct ring_buffer_desc *)((void *)trace_desc + trace_desc->struct_len); -- cgit v1.2.3