trace_uprobe: support reference counter in fd-based uprobe

This patch enables uprobes with reference counter in fd-based uprobe.
Highest 32 bits of perf_event_attr.config is used to stored offset
of the reference count (semaphore).

Format information in /sys/bus/event_source/devices/uprobe/format/ is
updated to reflect this new feature.

Link: http://lkml.kernel.org/r/20181002053636.1896903-1-songliubraving@fb.com

Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-and-tested-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

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,

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 = 32,
+	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:32-63");
+
+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,
 };
 
 static int perf_uprobe_event_init(struct perf_event *event)
 {
 	int err;
+	unsigned long ref_ctr_offset;
 	bool is_retprobe;
 
 	if (event->attr.type != perf_uprobe.type)
@@ -8463,7 +8491,8 @@ static int perf_uprobe_event_init(struct perf_event *event)
 		return -EOPNOTSUPP;
 
 	is_retprobe = event->attr.config & PERF_PROBE_CONFIG_IS_RETPROBE;
-	err = perf_uprobe_init(event, is_retprobe);
+	ref_ctr_offset = event->attr.config >> PERF_UPROBE_REF_CTR_OFFSET_SHIFT;
+	err = perf_uprobe_init(event, ref_ctr_offset, is_retprobe);
 	if (err)
 		return err;
 

kernel/trace/trace_event_perf.c

@@ -290,7 +290,8 @@ void perf_kprobe_destroy(struct perf_event *p_event)
 #endif /* CONFIG_KPROBE_EVENTS */
 
 #ifdef CONFIG_UPROBE_EVENTS
-int perf_uprobe_init(struct perf_event *p_event, bool is_retprobe)
+int perf_uprobe_init(struct perf_event *p_event,
+		     unsigned long ref_ctr_offset, bool is_retprobe)
 {
 	int ret;
 	char *path = NULL;
@@ -312,8 +313,8 @@ int perf_uprobe_init(struct perf_event *p_event, bool is_retprobe)
 		goto out;
 	}
 
-	tp_event = create_local_trace_uprobe(
-		path, p_event->attr.probe_offset, is_retprobe);
+	tp_event = create_local_trace_uprobe(path, p_event->attr.probe_offset,
+					     ref_ctr_offset, is_retprobe);
 	if (IS_ERR(tp_event)) {
 		ret = PTR_ERR(tp_event);
 		goto out;

kernel/trace/trace_probe.h

@@ -412,6 +412,7 @@ create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
 extern void destroy_local_trace_kprobe(struct trace_event_call *event_call);
 
 extern struct trace_event_call *
-create_local_trace_uprobe(char *name, unsigned long offs, bool is_return);
+create_local_trace_uprobe(char *name, unsigned long offs,
+			  unsigned long ref_ctr_offset, bool is_return);
 extern void destroy_local_trace_uprobe(struct trace_event_call *event_call);
 #endif

kernel/trace/trace_uprobe.c

@@ -1405,7 +1405,8 @@ static int unregister_uprobe_event(struct trace_uprobe *tu)
 
 #ifdef CONFIG_PERF_EVENTS
 struct trace_event_call *
-create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
+create_local_trace_uprobe(char *name, unsigned long offs,
+			  unsigned long ref_ctr_offset, bool is_return)
 {
 	struct trace_uprobe *tu;
 	struct path path;
@@ -1437,6 +1438,7 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
 
 	tu->offset = offs;
 	tu->path = path;
+	tu->ref_ctr_offset = ref_ctr_offset;
 	tu->filename = kstrdup(name, GFP_KERNEL);
 	init_trace_event_call(tu, &tu->tp.call);