On Fri, Jan 05, 2024 at 02:37:44PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
>
> If the kbuffer was read to completion, the kbuf->curr would equal both the
> size and kbuf->next. The kbuffer_refresh() is to update the kbuf if more
> data was added to the buffer. But if curr is at the end, the next pointer
> was not updated, which is incorrect. The next pointer needs to be moved to
> the end of the newly written event.
>
> Update the pointers in kbuffer_refresh() just as if it was loaded new (but
> still keeping curr at the correct location).
>
> Link: https://lore.kernel.org/linux-trace-devel/ZZfJQTOyl0dHiTU-@xxxxxxxxxx/
>
> Reported-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
> Fixes: 7a4d5b24 ("kbuffer: Add kbuffer_refresh() API")
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
> src/kbuffer-parse.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/src/kbuffer-parse.c b/src/kbuffer-parse.c
> index 4801d432c58c..1e1d168b534c 100644
> --- a/src/kbuffer-parse.c
> +++ b/src/kbuffer-parse.c
> @@ -299,6 +299,9 @@ void kbuffer_free(struct kbuffer *kbuf)
> free(kbuf);
> }
>
> +static unsigned int old_update_pointers(struct kbuffer *kbuf);
> +static unsigned int update_pointers(struct kbuffer *kbuf);
> +
> /**
> * kbuffer_refresh - update the meta data from the subbuffer
> * @kbuf; The kbuffer to update
> @@ -309,13 +312,24 @@ void kbuffer_free(struct kbuffer *kbuf)
> int kbuffer_refresh(struct kbuffer *kbuf)
> {
> unsigned long long flags;
> + unsigned int old_size;
>
> if (!kbuf || !kbuf->subbuffer)
> return -1;
>
> + old_size = kbuf->size;
> +
> flags = read_long(kbuf, kbuf->subbuffer + 8);
> kbuf->size = (unsigned int)flags & COMMIT_MASK;
>
> + /* Update next to be the next element */
> + if (kbuf->size != old_size && kbuf->curr == old_size) {
> + if (kbuf->flags & KBUFFER_FL_OLD_FORMAT)
> + old_update_pointers(kbuf);
> + else
> + update_pointers(kbuf);
> + }
> +
> return 0;
> }
I've been trying the new stack but I see some weird unexpected events:
$ echo 3 > /sys/kernel/debug/tracing/trace_marker
<...>-5 44401.178473328 mmiotrace_rw: 0 0 0 0 0 0 // I clearly didn't enable this event
<...>-208 44401.178473328 print: tracing_mark_write: 2
Looking closer at the kbuf I see before the kbuffer_refresh()
index = 244, curr = 272, next = 272, size = 272, start = 16
And after
index = 280, curr = 272, next = 280, size = 312, start = 16
Could this index be the problem as this is used in kbuffer_read_event()?
>
> --
> 2.42.0
>
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