This is a note to let you know that I've just added the patch titled
ring-buffer: Have saved event hold the entire event
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ring-buffer-have-saved-event-hold-the-entire-event.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From b049525855fdd0024881c9b14b8fbec61c3f53d3 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
Date: Tue, 12 Dec 2023 07:25:58 -0500
Subject: ring-buffer: Have saved event hold the entire event
From: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
commit b049525855fdd0024881c9b14b8fbec61c3f53d3 upstream.
For the ring buffer iterator (non-consuming read), the event needs to be
copied into the iterator buffer to make sure that a writer does not
overwrite it while the user is reading it. If a write happens during the
copy, the buffer is simply discarded.
But the temp buffer itself was not big enough. The allocation of the
buffer was only BUF_MAX_DATA_SIZE, which is the maximum data size that can
be passed into the ring buffer and saved. But the temp buffer needs to
hold the meta data as well. That would be BUF_PAGE_SIZE and not
BUF_MAX_DATA_SIZE.
Link: https://lore.kernel.org/linux-trace-kernel/20231212072558.61f76493@xxxxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Fixes: 785888c544e04 ("ring-buffer: Have rb_iter_head_event() handle concurrent writer")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/ring_buffer.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2275,7 +2275,7 @@ rb_iter_head_event(struct ring_buffer_it
*/
barrier();
- if ((iter->head + length) > commit || length > BUF_MAX_DATA_SIZE)
+ if ((iter->head + length) > commit || length > BUF_PAGE_SIZE)
/* Writer corrupted the read? */
goto reset;
@@ -4836,7 +4836,8 @@ ring_buffer_read_prepare(struct trace_bu
if (!iter)
return NULL;
- iter->event = kmalloc(BUF_MAX_DATA_SIZE, flags);
+ /* Holds the entire event: data and meta data */
+ iter->event = kmalloc(BUF_PAGE_SIZE, flags);
if (!iter->event) {
kfree(iter);
return NULL;
Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are
queue-5.10/ring-buffer-have-saved-event-hold-the-entire-event.patch
queue-5.10/ring-buffer-fix-memory-leak-of-free-page.patch
queue-5.10/ring-buffer-fix-a-race-in-rb_time_cmpxchg-for-32-bit-archs.patch
queue-5.10/tracing-update-snapshot-buffer-on-resize-if-it-is-allocated.patch
queue-5.10/ring-buffer-fix-writing-to-the-buffer-with-max_data_size.patch
