Re: [PATCH RESEND] trace_uprobe: support reference counter in fd-based uprobe

[Song Liu]

Hi Peter,


> On Sep 24, 2018, at 2:12 PM, Song Liu <songliubraving@xxxxxx> wrote:
> 
> This patch enables uprobes with reference counter in fd-based uprobe.
> Highest 40 bits of perf_event_attr.config is used to stored offset
> of the reference counter (semaphore).
> 
> Format information in /sys/bus/event_source/devices/uprobe/format/ is
> updated to reflect this new feature.
> 
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> Reviewed-and-tested-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Cc: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
> include/linux/trace_events.h    |  3 +-
> kernel/events/core.c            | 49 ++++++++++++++++++++++++++-------
> kernel/trace/trace_event_perf.c |  7 +++--
> kernel/trace/trace_probe.h      |  3 +-
> kernel/trace/trace_uprobe.c     |  4 ++-
> 5 files changed, 50 insertions(+), 16 deletions(-)
> 
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 78a010e19ed4..4130a5497d40 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -575,7 +575,8 @@ extern int bpf_get_kprobe_info(const struct perf_event *event,
> 			       bool perf_type_tracepoint);
> #endif
> #ifdef CONFIG_UPROBE_EVENTS
> -extern int  perf_uprobe_init(struct perf_event *event, bool is_retprobe);
> +extern int  perf_uprobe_init(struct perf_event *event,
> +			     unsigned long ref_ctr_offset, bool is_retprobe);
> extern void perf_uprobe_destroy(struct perf_event *event);
> extern int bpf_get_uprobe_info(const struct perf_event *event,
> 			       u32 *fd_type, const char **filename,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index c80549bf82c6..a4ad5235ec9b 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8368,30 +8368,39 @@ 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_BITS	# of bits in config as th offset
> + * PERF_UPROBE_REF_CTR_OFFSET_SHIFT	# of bits to shift left
>  */
> enum perf_probe_config {
> 	PERF_PROBE_CONFIG_IS_RETPROBE = 1U << 0,  /* [k,u]retprobe */
> +	PERF_UPROBE_REF_CTR_OFFSET_BITS = 40,
> +	PERF_UPROBE_REF_CTR_OFFSET_SHIFT = 64 - PERF_UPROBE_REF_CTR_OFFSET_BITS,
> };
> 
> PMU_FORMAT_ATTR(retprobe, "config:0");
> +#endif
> 
> -static struct attribute *probe_attrs[] = {
> +#ifdef CONFIG_KPROBE_EVENTS
> +static struct attribute *kprobe_attrs[] = {
> 	&format_attr_retprobe.attr,
> 	NULL,
> };
> 
> -static struct attribute_group probe_format_group = {
> +static struct attribute_group kprobe_format_group = {
> 	.name = "format",
> -	.attrs = probe_attrs,
> +	.attrs = kprobe_attrs,
> };
> 
> -static const struct attribute_group *probe_attr_groups[] = {
> -	&probe_format_group,
> +static const struct attribute_group *kprobe_attr_groups[] = {
> +	&kprobe_format_group,
> 	NULL,
> };
> -#endif
> 
> -#ifdef CONFIG_KPROBE_EVENTS
> static int perf_kprobe_event_init(struct perf_event *event);
> static struct pmu perf_kprobe = {
> 	.task_ctx_nr	= perf_sw_context,
> @@ -8401,7 +8410,7 @@ static struct pmu perf_kprobe = {
> 	.start		= perf_swevent_start,
> 	.stop		= perf_swevent_stop,
> 	.read		= perf_swevent_read,
> -	.attr_groups	= probe_attr_groups,
> +	.attr_groups	= kprobe_attr_groups,
> };
> 
> static int perf_kprobe_event_init(struct perf_event *event)
> @@ -8433,6 +8442,24 @@ static int perf_kprobe_event_init(struct perf_event *event)
> #endif /* CONFIG_KPROBE_EVENTS */
> 
> #ifdef CONFIG_UPROBE_EVENTS
> +PMU_FORMAT_ATTR(ref_ctr_offset, "config:63-24");

I guess you meant this part? This is for uprobe only, so I put
it here. 

Thanks,
Song

> +
> +static struct attribute *uprobe_attrs[] = {
> +	&format_attr_retprobe.attr,
> +	&format_attr_ref_ctr_offset.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group uprobe_format_group = {
> +	.name = "format",
> +	.attrs = uprobe_attrs,
> +};
> +
> +static const struct attribute_group *uprobe_attr_groups[] = {
> +	&uprobe_format_group,
> +	NULL,
> +};
> +
> static int perf_uprobe_event_init(struct perf_event *event);
> static struct pmu perf_uprobe = {
> 	.task_ctx_nr	= perf_sw_context,
> @@ -8442,12 +8469,13 @@ static struct pmu perf_uprobe = {
> 	.start		= perf_swevent_start,
> 	.stop		= perf_swevent_stop,
> 	.read		= perf_swevent_read,
> -	.attr_groups	= probe_attr_groups,
> +	.attr_groups	= uprobe_attr_groups,
> };
>