Re: [PATCH] perf/kprobe: maxactive for fd-based kprobe

[Song Liu <songliubraving@fb.com>]

> On Jun 9, 2022, at 12:29 PM, Dmitrii Dolgov <9erthalion6@gmail.com> wrote:
> 
> Enable specifying maxactive for fd based kretprobe. This will be useful
> for tracing tools like bcc and bpftrace (see for example discussion [1]).
> Use highest 12 bit (bit 52-63) to allow maximal maxactive of 4095.
> 
> The original patch [2] seems to be fallen through the cracks and wasn't
> applied. I've merely rebased the work done by Song Liu and verififed it
> still works.
> 
> [1]: https://github.com/iovisor/bpftrace/issues/835
> [2]: https://lore.kernel.org/all/20191007223111.1142454-1-songliubraving@fb.com/

Thanks for pulling this out of the cracks. :)

Since there isn't much change from [2], I think this should still show 
"From:" me, and with "Signed-off-by" both of us. 

And a nit below:

Thanks,
Song

> 
> Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
> ---
> include/linux/trace_events.h    |  3 ++-
> kernel/events/core.c            | 20 ++++++++++++++++----
> kernel/trace/trace_event_perf.c |  5 +++--
> kernel/trace/trace_kprobe.c     |  4 ++--
> kernel/trace/trace_probe.h      |  2 +-
> 5 files changed, 24 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index e6e95a9f07a5..7ca453a73252 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -850,7 +850,8 @@ extern void perf_trace_destroy(struct perf_event *event);
> extern int  perf_trace_add(struct perf_event *event, int flags);
> extern void perf_trace_del(struct perf_event *event, int flags);
> #ifdef CONFIG_KPROBE_EVENTS
> -extern int  perf_kprobe_init(struct perf_event *event, bool is_retprobe);
> +extern int  perf_kprobe_init(struct perf_event *event, bool is_retprobe,
> +			     int max_active);
> extern void perf_kprobe_destroy(struct perf_event *event);
> extern int bpf_get_kprobe_info(const struct perf_event *event,
> 			       u32 *fd_type, const char **symbol,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 23bb19716ad3..f0e936b3dfc4 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9809,24 +9809,34 @@ static struct pmu perf_tracepoint = {
>  * PERF_PROBE_CONFIG_IS_RETPROBE if set, create kretprobe/uretprobe
>  *                               if not set, create kprobe/uprobe
>  *
> - * The following values specify a reference counter (or semaphore in the
> - * terminology of tools like dtrace, systemtap, etc.) Userspace Statically
> - * Defined Tracepoints (USDT). Currently, we use 40 bit for the offset.
> + * PERF_UPROBE_REF_CTR_OFFSET_* specify a reference counter (or semaphore
> + * in the terminology of tools like dtrace, systemtap, etc.) Userspace
> + * Statically Defined Tracepoints (USDT). Currently, we use 40 bit for the

40 bit is not accurate anymore, let's fix it (32). 

Otherwise, LGTM. 

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