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

[Dmitrii Dolgov <9erthalion6@gmail.com>]

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/

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
+ * 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,
 };
@@ -9857,6 +9867,7 @@ 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;
@@ -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 = 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 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 *
-- 
2.32.0