Re: [PATCH] perf/kprobe: maxactive for fd-based kprobe (pmu perf_kprobe)

From: Steven Rostedt
Date: Wed Nov 13 2019 - 14:14:21 EST


[ Added Ingo ]

On Mon, 7 Oct 2019 15:31:11 -0700
Song Liu <songliubraving@xxxxxx> wrote:

> Enable specifying maxactive for fd based kretprobe. This will be useful
> for tracing tools like bcc and bpftrace. [1] discussed the need of this
> in bpftrace. Use highest highest 12 bit (bit 52-63) to allow maximal
> maxactive of 4095.
>
> [1] https://github.com/iovisor/bpftrace/issues/835
>
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

-- Steve


> ---
> 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 30a8cdcfd4a4..706d515d2b5e 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -581,7 +581,8 @@ 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 3f0cb82e4fbc..f1b16cda5a9b 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8772,24 +8772,34 @@ 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
> + * 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 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 = 12,
> + PERF_KPROBE_MAX_ACTIVE_SHIFT = 64 - PERF_KPROBE_MAX_ACTIVE_BITS,
> };
>
> PMU_FORMAT_ATTR(retprobe, "config:0");
> #endif
>
> #ifdef CONFIG_KPROBE_EVENTS
> +/* KRETPROBE_MAXACTIVE_MAX is 4096, only allow 4095 here to save a bit */
> +PMU_FORMAT_ATTR(max_active, "config:52-63");
> +
> static struct attribute *kprobe_attrs[] = {
> + &format_attr_max_active.attr,
> &format_attr_retprobe.attr,
> NULL,
> };
> @@ -8820,6 +8830,7 @@ static int perf_kprobe_event_init(struct perf_event *event)
> {
> int err;
> bool is_retprobe;
> + int max_active;
>
> if (event->attr.type != perf_kprobe.type)
> return -ENOENT;
> @@ -8834,7 +8845,8 @@ 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 = event->attr.config >> PERF_KPROBE_MAX_ACTIVE_SHIFT;
> + err = perf_kprobe_init(event, is_retprobe, max_active);
> if (err)
> return err;
>
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index 0892e38ed6fb..da6744ac7bc9 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -240,7 +240,8 @@ 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;
> @@ -266,7 +267,7 @@ 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 324ffbea3556..12088a76e7da 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1556,7 +1556,7 @@ 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)
> {
> struct trace_kprobe *tk;
> int ret;
> @@ -1570,7 +1570,7 @@ 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 4ee703728aec..b4368c652749 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -373,7 +373,7 @@ extern int traceprobe_set_print_fmt(struct trace_probe *tp, bool is_return);
> #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 *