linux-kernel - Re: [PATCH 01/13] perf: Simplify perf_event

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Date:   Wed, 15 Nov 2023 10:31:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Olsa <olsajiri@...il.com>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        namhyung@...nel.org, irogers@...gle.com, adrian.hunter@...el.com
Subject: Re: [PATCH 01/13] perf: Simplify perf_event_alloc() error path

On Fri, Nov 03, 2023 at 01:38:05PM +0100, Jiri Olsa wrote:

> > -err_callchain_buffer:
> > -	if (!event->parent) {
> > -		if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
> > -			put_callchain_buffers();
> > -	}
> 
> hum, so this is now called all the time via __free_event, but it should
> be called only if we passed get_callchain_buffers call.. this could screw
> up nr_callchain_events number eventually no?

Yes, good catch, thanks!

Something like the below should handle that, no?

---
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -628,14 +628,15 @@ struct swevent_hlist {
 	struct rcu_head			rcu_head;
 };
 
-#define PERF_ATTACH_CONTEXT	0x01
-#define PERF_ATTACH_GROUP	0x02
-#define PERF_ATTACH_TASK	0x04
-#define PERF_ATTACH_TASK_DATA	0x08
-#define PERF_ATTACH_ITRACE	0x10
-#define PERF_ATTACH_SCHED_CB	0x20
-#define PERF_ATTACH_CHILD	0x40
-#define PERF_ATTACH_EXCLUSIVE	0x80
+#define PERF_ATTACH_CONTEXT	0x0001
+#define PERF_ATTACH_GROUP	0x0002
+#define PERF_ATTACH_TASK	0x0004
+#define PERF_ATTACH_TASK_DATA	0x0008
+#define PERF_ATTACH_ITRACE	0x0010
+#define PERF_ATTACH_SCHED_CB	0x0020
+#define PERF_ATTACH_CHILD	0x0040
+#define PERF_ATTACH_EXCLUSIVE	0x0080
+#define PERF_ATTACH_CALLCHAIN	0x0100
 
 struct bpf_prog;
 struct perf_cgroup;
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5166,10 +5166,8 @@ static void perf_addr_filters_splice(str
 /* vs perf_event_alloc() error */
 static void __free_event(struct perf_event *event)
 {
-	if (!event->parent) {
-		if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
-			put_callchain_buffers();
-	}
+	if (event->attach_state & PERF_ATTACH_CALLCHAIN)
+		put_callchain_buffers();
 
 	kfree(event->addr_filter_ranges);
 
@@ -12065,6 +12063,7 @@ perf_event_alloc(struct perf_event_attr
 			err = get_callchain_buffers(attr->sample_max_stack);
 			if (err)
 				goto err;
+			event->attach_state |= PERF_ATTACH_CALLCHAIN;
 		}
 	}