Re: [PATCH v4 1/1] perf/kprobe: maxactive for fd-based kprobe

[Steven Rostedt]

Peter,

Since this is mostly perf related, care to take it?

-- Steve


On Thu, 14 Jul 2022 21:34:03 +0200
Dmitrii Dolgov <9erthalion6@xxxxxxxxx> wrote:

> From: Song Liu <songliubraving@xxxxxx>
> 
> 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 4 bit (bit 59-63) to allow specifying maxactive by log2.
> 
> 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, verififed it
> still works, and modified to allow specifying maxactive by log2 per
> suggestion from the discussion thread.
> 
> Note that changes in rethook implementation may render maxactive
> obsolete.
> 
> [1]: https://github.com/iovisor/bpftrace/issues/835
> [2]: https://lore.kernel.org/all/20191007223111.1142454-1-songliubraving@xxxxxx/
> 
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> Signed-off-by: Dmitrii Dolgov <9erthalion6@xxxxxxxxx>
> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> Acked-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
> Previous discussion: https://lore.kernel.org/bpf/20220625152429.27539-1-9erthalion6@xxxxxxxxx/
> 
> Resent with LKML in Cc instead of linux-perf-users, as it is a kernel
> change.
> 
> Changes in v4:
>     - Allow specifying maxactive by log2
> 
> Changes in v3:
>     - Set correct author
> 
> Changes in v2:
>     - Fix comment about number bits for the offset
> 
>  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..184325ff2656 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 32 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
> + *
> + * PERF_KPROBE_MAX_ACTIVE_* defines log2 of max_active for kretprobe.
> + * KRETPROBE_MAXACTIVE_MAX is 4096. We allow 4095 here to save a bit.
>   */
>  enum perf_probe_config {
>  	PERF_PROBE_CONFIG_IS_RETPROBE = 1U << 0,  /* [k,u]retprobe */
>  	PERF_UPROBE_REF_CTR_OFFSET_BITS = 32,
>  	PERF_UPROBE_REF_CTR_OFFSET_SHIFT = 64 - PERF_UPROBE_REF_CTR_OFFSET_BITS,
> +	PERF_KPROBE_MAX_ACTIVE_BITS = 4,
> +	PERF_KPROBE_MAX_ACTIVE_SHIFT = 64 - PERF_KPROBE_MAX_ACTIVE_BITS,
>  };
>  
>  PMU_FORMAT_ATTR(retprobe, "config:0");
>  #endif
>  
>  #ifdef CONFIG_KPROBE_EVENTS
> +/* max_active is specified by log2, to allow larger values if needed */
> +PMU_FORMAT_ATTR(max_active_log2, "config:59-63");
> +
>  static struct attribute *kprobe_attrs[] = {
> +	&format_attr_max_active_log2.attr,
>  	&format_attr_retprobe.attr,
>  	NULL,
>  };
> @@ -9857,6 +9867,7 @@ static int perf_kprobe_event_init(struct perf_event *event)
>  {
>  	int err;
>  	bool is_retprobe;
> +	int max_active_log2;
>  
>  	if (event->attr.type != perf_kprobe.type)
>  		return -ENOENT;
> @@ -9871,7 +9882,8 @@ static int perf_kprobe_event_init(struct perf_event *event)
>  		return -EOPNOTSUPP;
>  
>  	is_retprobe = event->attr.config & PERF_PROBE_CONFIG_IS_RETPROBE;
> -	err = perf_kprobe_init(event, is_retprobe);
> +	max_active_log2 = event->attr.config >> PERF_KPROBE_MAX_ACTIVE_SHIFT;
> +	err = perf_kprobe_init(event, is_retprobe, 1U << max_active_log2);
>  	if (err)
>  		return err;
>  
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index a114549720d6..129000327809 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -245,7 +245,8 @@ void perf_trace_destroy(struct perf_event *p_event)
>  }
>  
>  #ifdef CONFIG_KPROBE_EVENTS
> -int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe)
> +int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe,
> +					 int max_active)
>  {
>  	int ret;
>  	char *func = NULL;
> @@ -271,7 +272,7 @@ int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe)
>  
>  	tp_event = create_local_trace_kprobe(
>  		func, (void *)(unsigned long)(p_event->attr.kprobe_addr),
> -		p_event->attr.probe_offset, is_retprobe);
> +		p_event->attr.probe_offset, is_retprobe, max_active);
>  	if (IS_ERR(tp_event)) {
>  		ret = PTR_ERR(tp_event);
>  		goto out;
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 47cebef78532..3ad30cfce9c3 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1784,7 +1784,7 @@ static int unregister_kprobe_event(struct trace_kprobe *tk)
>  /* create a trace_kprobe, but don't add it to global lists */
>  struct trace_event_call *
>  create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> -			  bool is_return)
> +			  bool is_return, int max_active)
>  {
>  	enum probe_print_type ptype;
>  	struct trace_kprobe *tk;
> @@ -1799,7 +1799,7 @@ create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
>  	event = func ? func : "DUMMY_EVENT";
>  
>  	tk = alloc_trace_kprobe(KPROBE_EVENT_SYSTEM, event, (void *)addr, func,
> -				offs, 0 /* maxactive */, 0 /* nargs */,
> +				offs, max_active, 0 /* nargs */,
>  				is_return);
>  
>  	if (IS_ERR(tk)) {
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index 92cc149af0fd..26fe21980793 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -376,7 +376,7 @@ extern int traceprobe_set_print_fmt(struct trace_probe *tp, enum probe_print_typ
>  #ifdef CONFIG_PERF_EVENTS
>  extern struct trace_event_call *
>  create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> -			  bool is_return);
> +			  bool is_return, int max_active);
>  extern void destroy_local_trace_kprobe(struct trace_event_call *event_call);
>  
>  extern struct trace_event_call *