On Sat, Jun 18, 2022 at 01:31:01PM +0800, chuang wrote: > Hi John, > > On Sat, Jun 18, 2022 at 12:13 PM John Fastabend > <john.fastabend@xxxxxxxxx> wrote: > > > > Chuang W wrote: > > > In a scenario where livepatch and aggrprobe coexist, the creating > > > kprobe_event using tracefs API will succeed, a trace event (e.g. > > > /debugfs/tracing/events/kprobe/XX) will exist, but perf_event_open() > > > will return an error. > > > > This seems a bit strange from API side. I'm not really familiar with > > livepatch, but I guess this is UAPI now so fixing add_kprobe_event_legacy > > to fail is not an option? > > > > The legacy kprobe API (i.e. tracefs API) has two steps: > > 1) register_kprobe > $ echo 'p:mykprobe XXX' > /sys/kernel/debug/tracing/kprobe_events > This will create a trace event of mykprobe and register a disable > kprobe that waits to be activated. > > 2) enable_kprobe > 2.1) using syscall perf_event_open > as the following code, perf_event_kprobe_open_legacy (file: > tools/lib/bpf/libbpf.c): > --- > attr.type = PERF_TYPE_TRACEPOINT; > pfd = syscall(__NR_perf_event_open, &attr, > pid < 0 ? -1 : pid, /* pid */ > pid == -1 ? 0 : -1, /* cpu */ > -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC); > --- > In the implementation code of perf_event_open, enable_kprobe() will be executed. > 2.2) using shell > $ echo 1 > /sys/kernel/debug/tracing/events/kprobes/mykprobe/enable > As with perf_event_open, enable_kprobe() will also be executed. > > When using the same function XXX, kprobe and livepatch cannot coexist, > that is, step 2) will return an error (ref: arm_kprobe_ftrace()), just curious.. is that because of ipmodify flag on ftrace_ops? AFAICS that be a poblem just for kretprobes, cc-ing Masami thanks, jirka > however, step 1) is ok! > However, the new kprobe API (i.e. perf kprobe API) aggregates > register_kprobe and enable_kprobe, internally fixes the issue on > failed enable_kprobe. > But above all, for the legacy kprobe API, I think it should remove > kprobe_event on failed add_kprobe_event_legacy() in > perf_event_kprobe_open_legacy (file: tools/lib/bpf/libbpf.c).
