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/XXX) will exist, but
perf_event_open() will return an error because both livepatch and kprobe
use FTRACE_OPS_FL_IPMODIFY. As follows:
1) add a livepatch
$ insmod livepatch-XXX.ko
2) add a kprobe using tracefs API (i.e. add_kprobe_event_legacy)
$ echo 'p:mykprobe XXX' > /sys/kernel/debug/tracing/kprobe_events
3) enable this kprobe (i.e. sys_perf_event_open)
This will return an error, -EBUSY.
On Andrii Nakryiko's comment, few error paths in
bpf_program__attach_kprobe_opts() which should need to call
remove_kprobe_event_legacy().
With this patch, whenever an error is returned after
add_kprobe_event_legacy() or bpf_program__attach_perf_event_opts(), this
ensures that the created kprobe_event is cleaned.
Signed-off-by: Chuang W <nashuiliang@xxxxxxxxx>
Signed-off-by: Jingren Zhou <zhoujingren@xxxxxxxxxxxxxx>
---
V2->v3:
- add detail commits
- call remove_kprobe_event_legacy() on failed bpf_program__attach_perf_event_opts()
tools/lib/bpf/libbpf.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 49e359cd34df..038b0cb3313f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10811,10 +10811,11 @@ 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;
@@ -10828,9 +10829,14 @@ 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 legacy kprobe_event */
+ remove_kprobe_event_legacy(probe_name, retprobe);
+ return err;
}
struct bpf_link *
@@ -10899,6 +10905,9 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
return link;
err_out:
+ /* Clear the newly added legacy kprobe_event */
+ if (legacy)
+ remove_kprobe_event_legacy(legacy_probe, retprobe);
free(legacy_probe);
return libbpf_err_ptr(err);
}
--
2.34.1
