netdev - [PATCH v2] libbpf: Cleanup the kprobe_event on failed add_kprobe_event

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Date:   Tue, 21 Jun 2022 15:32:33 +0800
From:   Chuang W <nashuiliang@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Chuang W <nashuiliang@...il.com>,
        Jingren Zhou <zhoujingren@...iglobal.com>
Subject: [PATCH v2] libbpf: Cleanup the kprobe_event on failed add_kprobe_event_legacy()

Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
livepatch"), in a scenario where livepatch and kprobe coexist on the
same function entry, the creation of kprobe_event using
add_kprobe_event_legacy() will be successful, at the same time as a
trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
perf_event_open() will return an error because both livepatch and kprobe
use FTRACE_OPS_FL_IPMODIFY.

With this patch, whenever an error is returned after
add_kprobe_event_legacy(), this ensures that the created kprobe_event is
cleaned.

Signed-off-by: Chuang W <nashuiliang@...il.com>
Signed-off-by: Jingren Zhou <zhoujingren@...iglobal.com>
---
 tools/lib/bpf/libbpf.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0781fae58a06..d0a36350e22a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10809,10 +10809,11 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
 	}
 	type = determine_kprobe_perf_type_legacy(probe_name, retprobe);
 	if (type < 0) {
+		err = type;
 		pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",
 			kfunc_name, offset,
-			libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
-		return type;
+			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+		goto clear_kprobe_event;
 	}
 	attr.size = sizeof(attr);
 	attr.config = type;
@@ -10826,9 +10827,14 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
 		err = -errno;
 		pr_warn("legacy kprobe perf_event_open() failed: %s\n",
 			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
-		return err;
+		goto clear_kprobe_event;
 	}
 	return pfd;
+
+clear_kprobe_event:
+	/* Clear the newly added kprobe_event */
+	remove_kprobe_event_legacy(probe_name, retprobe);
+	return err;
 }
 
 struct bpf_link *
-- 
2.34.1