Re: [PATCH v2] tracing/uprobe: Add missing PID filter for uretprobe

Oleg Nesterov
2024-09-06T19:18:37Z

On 09/06, Jiri Olsa wrote:
>
> On Mon, Sep 02, 2024 at 03:22:25AM +0800, Tianyi Liu wrote:
> >
> > For now, please forget the original patch as we need a new solution ;)
>
> hi,
> any chance we could go with your fix until we find better solution?

Well, as I said from the very beginning I won't really argue even if
I obviously don't like this change very much. As long as the changelog /
comments clearly explain this change. I understand that sometimes an
ugly/incomplete/whatever workaround is better than nothing.

> it's simple and it fixes most of the cases for return uprobe pid filter
> for events with bpf programs..

But to remind it doesn't even fixes all the filtering problems with uprobes,
not uretprobes,

> I know during the discussion we found
> that standard perf record path won't work if there's bpf program
> attached on the same event,

Ah. Yes, this is another problem I tried to point out. But if we discuss
the filtering we can forget about /usr/bin/perf.

Again, again, again, I know nothing about bpf. But it seems to me that
perf_event_attach_bpf_prog() allows to attach up to BPF_TRACE_MAX_PROGS
progs to event->tp_event->prog_array, and then bpf_prog_run_array_uprobe()
should run them all. Right?

So I think that if you run 2 instances of run_prog from my last test-case
with $PID1 and $PID2, the filtering will be broken again. Both instances
will share the same trace_event_call and the same trace_uprobe_filter.

> and also it's not a common use case

OK.

And btw... Can bpftrace attach to the uprobe tp?

# perf probe -x ./test -a func
Added new event:
probe_test:func (on func in /root/TTT/test)

You can now use it in all perf tools, such as:

perf record -e probe_test:func -aR sleep 1

# bpftrace -e 'tracepoint:probe_test:func { printf("%d\n", pid); }'
Attaching 1 probe...
ioctl(PERF_EVENT_IOC_SET_BPF): Invalid argument
ERROR: Error attaching probe: tracepoint:probe_test:func

Oleg.