linux-kernel - Fix repeated legacy kprobes on same function

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Message-ID: <c84094d2-75c1-a50d-ea9e-9dded5f01fb9@bytedance.com>
Date:   Fri, 24 Dec 2021 12:01:06 +0800
From:   Qiang Wang <wangqiang.wq.frank@...edance.com>
To:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org,
        zhouchengming@...edance.com, songmuchun@...edance.com,
        duanxiongchun@...edance.com, shekairui@...edance.com
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Fix repeated legacy kprobes on same function

If repeated legacy kprobes on same function in one process,
libbpf will register using the same probe name and got -EBUSY
error. So append index to the probe name format to fix this
problem.

And fix a bug in commit 46ed5fc33db9, which wrongly used the
func_name instead of probe_name to register.

Fixes: 46ed5fc33db9 ("libbpf: Refactor and simplify legacy kprobe code")
Co-developed-by: Chengming Zhou <zhouchengming@...edance.com>
Signed-off-by: Qiang Wang <wangqiang.wq.frank@...edance.com>
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>

---
  tools/lib/bpf/libbpf.c | 5 +++--
  1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7c74342bb668..7d1097958459 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9634,7 +9634,8 @@ static int append_to_file(const char *file, const 
char *fmt, ...)
  static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
                                          const char *kfunc_name, size_t 
offset)
  {
-       snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), 
kfunc_name, offset);
+       static int index = 0;
+       snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx_%d", getpid(), 
kfunc_name, offset, index++);
  }

  static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,
@@ -9735,7 +9736,7 @@ bpf_program__attach_kprobe_opts(const struct 
bpf_program *prog,
                 gen_kprobe_legacy_event_name(probe_name, 
sizeof(probe_name),
                                              func_name, offset);

-               legacy_probe = strdup(func_name);
+               legacy_probe = strdup(probe_name);
                 if (!legacy_probe)
                         return libbpf_err_ptr(-ENOMEM);

--
2.20.1