Messages in this thread Patch in this message | | | From | Chuang W <> | Subject | [PATCH v3] libbpf: Cleanup the legacy kprobe_event on failed add/attach_event() | Date | Sun, 26 Jun 2022 11:13:01 +0800 |
| |
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@gmail.com> Signed-off-by: Jingren Zhou <zhoujingren@didiglobal.com> --- 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
| |